# HG changeset patch
# Parent  f986e55c4e0b41c6b50bd74d287614b564d7895f
Bug 1077651. Measure frame uniformity tests. r=kats

diff --git a/dom/base/nsDOMWindowUtils.cpp b/dom/base/nsDOMWindowUtils.cpp
--- a/dom/base/nsDOMWindowUtils.cpp
+++ b/dom/base/nsDOMWindowUtils.cpp
@@ -64,28 +64,29 @@
 #include <algorithm>
 
 #if defined(MOZ_X11) && defined(MOZ_WIDGET_GTK)
 #include <gdk/gdk.h>
 #include <gdk/gdkx.h>
 #endif
 
 #include "Layers.h"
-#include "mozilla/layers/ShadowLayers.h"
 #include "gfxPrefs.h"
 
 #include "mozilla/dom/Element.h"
 #include "mozilla/dom/TabChild.h"
 #include "mozilla/dom/IDBFactoryBinding.h"
 #include "mozilla/dom/IDBMutableFileBinding.h"
 #include "mozilla/dom/indexedDB/IDBMutableFile.h"
 #include "mozilla/dom/indexedDB/IndexedDatabaseManager.h"
 #include "mozilla/dom/PermissionMessageUtils.h"
 #include "mozilla/dom/quota/PersistenceType.h"
 #include "mozilla/dom/quota/QuotaManager.h"
+#include "mozilla/layers/FrameUniformityData.h"
+#include "mozilla/layers/ShadowLayers.h"
 #include "nsPrintfCString.h"
 #include "nsViewportInfo.h"
 #include "nsIFormControl.h"
 #include "nsIScriptError.h"
 #include "nsIAppShell.h"
 #include "nsWidgetsCID.h"
 #include "FrameLayerBuilder.h"
 #include "nsDisplayList.h"
@@ -3708,16 +3709,37 @@ nsDOMWindowUtils::SetChromeMargin(int32_
       }
     }
   }
 
   return NS_OK;
 }
 
 NS_IMETHODIMP
+nsDOMWindowUtils::GetFrameUniformityTestData(JSContext* aContext,
+                                             JS::MutableHandleValue aOutFrameUniformity)
+{
+  MOZ_RELEASE_ASSERT(nsContentUtils::IsCallerChrome());
+  nsIWidget* widget = GetWidget();
+  if (!widget) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  nsRefPtr<LayerManager> manager = widget->GetLayerManager();
+  if (!manager) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  FrameUniformityData outData;
+  manager->GetFrameUniformity(&outData);
+  outData.ToJS(aOutFrameUniformity, aContext);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
 nsDOMWindowUtils::XpconnectArgument(nsIDOMWindowUtils* aThis)
 {
   // Do nothing.
   return NS_OK;
 }
 
 NS_IMETHODIMP
 nsDOMWindowUtils::AskPermission(nsIContentPermissionRequest* aRequest)
diff --git a/dom/interfaces/base/nsIDOMWindowUtils.idl b/dom/interfaces/base/nsIDOMWindowUtils.idl
--- a/dom/interfaces/base/nsIDOMWindowUtils.idl
+++ b/dom/interfaces/base/nsIDOMWindowUtils.idl
@@ -1807,16 +1807,24 @@ interface nsIDOMWindowUtils : nsISupport
                        in int32_t aRight,
                        in int32_t aBottom,
                        in int32_t aLeft);
 
   /**
    * Enable some service workers testing features.
    */
   attribute boolean serviceWorkersTestingEnabled;
+
+  /**
+   * Returns a JSObject which contains a list of frame uniformities
+   * when the pref gfx.vsync.collect-scroll-data is enabled.
+   * Every result contains a layer address and a frame uniformity for that layer.
+   * A negative value indicate an invalid frame uniformity and an error has occured.
+   */
+  [implicit_jscontext] jsval getFrameUniformityTestData();
 };
 
 [scriptable, uuid(c694e359-7227-4392-a138-33c0cc1f15a6)]
 interface nsITranslationNodeList : nsISupports {
   readonly attribute unsigned long length;
   nsIDOMNode item(in unsigned long index);
 
   // A translation root is a block element, or an inline element
diff --git a/dom/webidl/APZTestData.webidl b/dom/webidl/APZTestData.webidl
--- a/dom/webidl/APZTestData.webidl
+++ b/dom/webidl/APZTestData.webidl
@@ -29,9 +29,19 @@ dictionary APZBucket {
   unsigned long sequenceNumber;
   sequence<ScrollFrameData> scrollFrames;
 };
 
 // All the paints and repaint requests. This is the top-level data structure.
 dictionary APZTestData {
   sequence<APZBucket> paints;
   sequence<APZBucket> repaintRequests;
-};
\ No newline at end of file
+};
+
+// A frame uniformity measurement for every scrollable layer
+dictionary FrameUniformity {
+  unsigned long layerAddress;
+  float frameUniformity;
+};
+
+dictionary FrameUniformityResults {
+  sequence<FrameUniformity> layerUniformities;
+};
diff --git a/gfx/2d/BasePoint.h b/gfx/2d/BasePoint.h
--- a/gfx/2d/BasePoint.h
+++ b/gfx/2d/BasePoint.h
@@ -53,16 +53,19 @@ struct BasePoint {
     return *static_cast<Sub*>(this);
   }
   Sub& operator-=(const Sub& aPoint) {
     x -= aPoint.x;
     y -= aPoint.y;
     return *static_cast<Sub*>(this);
   }
 
+  Sub operator*(const Sub& aPoint) const {
+    return Sub(x * aPoint.x, y * aPoint.y);
+  }
   Sub operator*(T aScale) const {
     return Sub(x * aScale, y * aScale);
   }
   Sub operator/(T aScale) const {
     return Sub(x / aScale, y / aScale);
   }
 
   Sub operator-() const {
diff --git a/gfx/layers/Layers.h b/gfx/layers/Layers.h
--- a/gfx/layers/Layers.h
+++ b/gfx/layers/Layers.h
@@ -88,16 +88,17 @@ class ReadbackLayer;
 class ReadbackProcessor;
 class RefLayer;
 class LayerComposite;
 class ShadowableLayer;
 class ShadowLayerForwarder;
 class LayerManagerComposite;
 class SpecificLayerAttributes;
 class Compositor;
+class FrameUniformityData;
 
 namespace layerscope {
 class LayersPacket;
 }
 
 #define MOZ_LAYER_DECL_NAME(n, e)                              \
   virtual const char* Name() const override { return n; }  \
   virtual LayerType GetType() const override { return e; }
@@ -639,16 +640,17 @@ public:
     // LayersBackend::LAYERS_NONE is an error state, but in that case we should try to
     // avoid loading the compositor!
     return LayersBackend::LAYERS_BASIC != aBackend && LayersBackend::LAYERS_NONE != aBackend;
   }
 
   virtual bool IsCompositingCheap() { return true; }
 
   bool IsInTransaction() const { return mInTransaction; }
+  virtual void GetFrameUniformity(FrameUniformityData* aOutData) { }
   virtual bool RequestOverfill(mozilla::dom::OverfillCallback* aCallback) { return true; }
   virtual void RunOverfillCallback(const uint32_t aOverfill) { }
 
   virtual void SetRegionToClear(const nsIntRegion& aRegion)
   {
     mRegionToClear = aRegion;
   }
 
diff --git a/gfx/layers/apz/test/chrome.ini b/gfx/layers/apz/test/chrome.ini
new file mode 100644
--- /dev/null
+++ b/gfx/layers/apz/test/chrome.ini
@@ -0,0 +1,7 @@
+[DEFAULT]
+support-files =
+  apz_test_native_event_utils.js
+tags = apz-chrome
+
+[test_smoothness.html]
+skip-if = debug || (os != 'mac' && os != 'win') || !e10s # hardware vsync only on win/mac
diff --git a/gfx/layers/apz/test/test_smoothness.html b/gfx/layers/apz/test/test_smoothness.html
new file mode 100644
--- /dev/null
+++ b/gfx/layers/apz/test/test_smoothness.html
@@ -0,0 +1,77 @@
+<html>
+<head>
+  <title>Test Frame Uniformity While Scrolling</title>
+  <script type="text/javascript"
+          src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"></script>
+  <script type="application/javascript"
+          src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="application/javascript" src="apz_test_native_event_utils.js"></script>
+
+  <style>
+  #content {
+    height: 5000px;
+    background: repeating-linear-gradient(#EEE, #EEE 100px, #DDD 100px, #DDD 200px);
+  }
+  </style>
+  <script type="text/javascript">
+    var scrollEvents = 100;
+    var i = 0;
+    var testPref = "gfx.vsync.collect-scroll-transforms";
+    // Scroll points
+    var x = 100;
+    var y = 150;
+
+    SimpleTest.waitForExplicitFinish();
+    var utils = _getDOMWindowUtils(window);
+
+    function sendScrollEvent(aRafTimestamp) {
+      var scrollDiv = document.getElementById("content");
+
+      if (i < scrollEvents) {
+        i++;
+        // Scroll diff
+        var dx = 0;
+        var dy = -10; // Negative to scroll down
+        synthesizeNativeWheelAndWaitForEvent(scrollDiv, x, y, dx, dy);
+        window.requestAnimationFrame(sendScrollEvent);
+      } else {
+        // Locally, with silk and apz + e10s, retina 15" mbp usually get ~1.0 - 1.5
+        // w/o silk + e10s + apz, I get up to 7. Lower is better.
+        // Windows, I get ~3. Values are not valid w/o hardware vsync
+        var uniformities = _getDOMWindowUtils().getFrameUniformityTestData();
+        for (var j = 0; j < uniformities.layerUniformities.length; j++) {
+          var layerResult = uniformities.layerUniformities[j];
+          var layerAddr = layerResult.layerAddress;
+          var uniformity = layerResult.frameUniformity;
+          var msg = "Layer: " + layerAddr.toString(16) + " Uniformity: " + uniformity;
+          SimpleTest.ok((uniformity >= 0) && (uniformity < 4.0), msg);
+        }
+        SimpleTest.finish();
+      }
+    }
+
+    function startTest() {
+      window.requestAnimationFrame(sendScrollEvent);
+    }
+
+    window.onload = function() {
+      var apzEnabled = SpecialPowers.getBoolPref("layers.async-pan-zoom.enabled");
+      if (!apzEnabled) {
+        SimpleTest.ok(true, "APZ not enabled, skipping test");
+        SimpleTest.finish();
+      }
+
+      SpecialPowers.pushPrefEnv({
+        "set" : [
+          [testPref, true]
+        ]
+      }, startTest);
+    }
+    </script>
+</head>
+
+<body>
+  <div id="content">
+  </div>
+</body>
+</html>
diff --git a/gfx/layers/client/ClientLayerManager.cpp b/gfx/layers/client/ClientLayerManager.cpp
--- a/gfx/layers/client/ClientLayerManager.cpp
+++ b/gfx/layers/client/ClientLayerManager.cpp
@@ -9,16 +9,17 @@
 #include "mozilla/Assertions.h"         // for MOZ_ASSERT, etc
 #include "mozilla/Hal.h"
 #include "mozilla/dom/ScreenOrientation.h"  // for ScreenOrientation
 #include "mozilla/dom/TabChild.h"       // for TabChild
 #include "mozilla/hal_sandbox/PHal.h"   // for ScreenConfiguration
 #include "mozilla/layers/CompositableClient.h"
 #include "mozilla/layers/CompositorChild.h" // for CompositorChild
 #include "mozilla/layers/ContentClient.h"
+#include "mozilla/layers/FrameUniformityData.h"
 #include "mozilla/layers/ISurfaceAllocator.h"
 #include "mozilla/layers/LayersMessages.h"  // for EditReply, etc
 #include "mozilla/layers/LayersSurfaces.h"  // for SurfaceDescriptor
 #include "mozilla/layers/PLayerChild.h"  // for PLayerChild
 #include "mozilla/layers/LayerTransactionChild.h"
 #include "mozilla/layers/TextureClientPool.h" // for TextureClientPool
 #include "ClientReadbackLayer.h"        // for ClientReadbackLayer
 #include "nsAString.h"
@@ -421,16 +422,30 @@ ClientLayerManager::RequestProperty(cons
 void
 ClientLayerManager::StartNewRepaintRequest(SequenceNumber aSequenceNumber)
 {
   if (gfxPrefs::APZTestLoggingEnabled()) {
     mApzTestData.StartNewRepaintRequest(aSequenceNumber);
   }
 }
 
+void
+ClientLayerManager::GetFrameUniformity(FrameUniformityData* aOutData)
+{
+  MOZ_ASSERT(XRE_IsParentProcess(), "Frame Uniformity only supported in parent process");
+
+  if (HasShadowManager()) {
+    CompositorChild* child = GetRemoteRenderer();
+    child->SendGetFrameUniformity(aOutData);
+    return;
+  }
+
+  return LayerManager::GetFrameUniformity(aOutData);
+}
+
 bool
 ClientLayerManager::RequestOverfill(mozilla::dom::OverfillCallback* aCallback)
 {
   MOZ_ASSERT(aCallback != nullptr);
   MOZ_ASSERT(HasShadowManager(), "Request Overfill only supported on b2g for now");
 
   if (HasShadowManager()) {
     CompositorChild* child = GetRemoteRenderer();
diff --git a/gfx/layers/client/ClientLayerManager.h b/gfx/layers/client/ClientLayerManager.h
--- a/gfx/layers/client/ClientLayerManager.h
+++ b/gfx/layers/client/ClientLayerManager.h
@@ -29,16 +29,17 @@
 
 namespace mozilla {
 namespace layers {
 
 class ClientPaintedLayer;
 class CompositorChild;
 class ImageLayer;
 class PLayerChild;
+class FrameUniformityData;
 class TextureClientPool;
 
 class ClientLayerManager final : public LayerManager
 {
   typedef nsTArray<nsRefPtr<Layer> > LayerRefArray;
 
 public:
   explicit ClientLayerManager(nsIWidget* aWidget);
@@ -195,16 +196,17 @@ public:
 
   void SetNeedsComposite(bool aNeedsComposite)
   {
     mNeedsComposite = aNeedsComposite;
   }
   bool NeedsComposite() const { return mNeedsComposite; }
 
   virtual void Composite() override;
+  virtual void GetFrameUniformity(FrameUniformityData* aFrameUniformityData) override;
   virtual bool RequestOverfill(mozilla::dom::OverfillCallback* aCallback) override;
   virtual void RunOverfillCallback(const uint32_t aOverfill) override;
 
   virtual void DidComposite(uint64_t aTransactionId);
 
   virtual bool SupportsMixBlendModes(EnumSet<gfx::CompositionOp>& aMixBlendModes) override
   {
    return (GetTextureFactoryIdentifier().mSupportedBlendModes & aMixBlendModes) == aMixBlendModes;
diff --git a/gfx/layers/composite/AsyncCompositionManager.cpp b/gfx/layers/composite/AsyncCompositionManager.cpp
--- a/gfx/layers/composite/AsyncCompositionManager.cpp
+++ b/gfx/layers/composite/AsyncCompositionManager.cpp
@@ -32,16 +32,17 @@
 #include "nsTArray.h"                   // for nsTArray, nsTArray_Impl, etc
 #include "nsTArrayForwardDeclare.h"     // for InfallibleTArray
 #include "UnitTransforms.h"             // for TransformTo
 #if defined(MOZ_WIDGET_ANDROID)
 # include <android/log.h>
 # include "AndroidBridge.h"
 #endif
 #include "GeckoProfiler.h"
+#include "FrameUniformityData.h"
 
 struct nsCSSValueSharedList;
 
 namespace mozilla {
 namespace layers {
 
 using namespace mozilla::gfx;
 
@@ -89,16 +90,28 @@ WalkTheTree(Layer* aLayer,
     }
   }
   for (Layer* child = aLayer->GetFirstChild();
        child; child = child->GetNextSibling()) {
     WalkTheTree<OP>(child, aReady, aTargetConfig);
   }
 }
 
+AsyncCompositionManager::AsyncCompositionManager(LayerManagerComposite* aManager)
+  : mLayerManager(aManager)
+  , mIsFirstPaint(true)
+  , mLayersUpdated(false)
+  , mReadyForCompose(true)
+{
+}
+
+AsyncCompositionManager::~AsyncCompositionManager()
+{
+}
+
 void
 AsyncCompositionManager::ResolveRefLayers()
 {
   if (!mLayerManager->GetRoot()) {
     return;
   }
 
   mReadyForCompose = true;
@@ -540,16 +553,45 @@ SampleAPZAnimations(const LayerMetricsWr
 
   if (AsyncPanZoomController* apzc = aLayer.GetApzc()) {
     activeAnimations |= apzc->AdvanceAnimations(aSampleTime);
   }
 
   return activeAnimations;
 }
 
+void
+AsyncCompositionManager::RecordShadowTransforms(Layer* aLayer)
+{
+  MOZ_ASSERT(gfxPrefs::CollectScrollTransforms());
+  MOZ_ASSERT(CompositorParent::IsInCompositorThread());
+
+  for (Layer* child = aLayer->GetFirstChild();
+      child; child = child->GetNextSibling()) {
+      RecordShadowTransforms(child);
+  }
+
+  for (uint32_t i = 0; i < aLayer->GetFrameMetricsCount(); i++) {
+    AsyncPanZoomController* apzc = aLayer->GetAsyncPanZoomController(i);
+    if (!apzc) {
+      continue;
+    }
+    gfx::Matrix4x4 shadowTransform = aLayer->AsLayerComposite()->GetShadowTransform();
+    if (!shadowTransform.Is2D()) {
+      continue;
+    }
+
+    Matrix transform = shadowTransform.As2D();
+    if (transform.IsTranslation() && !shadowTransform.IsIdentity()) {
+      Point translation = transform.GetTranslation();
+      mFrameUniformityData.RecordTransform(aLayer, translation);
+    }
+  }
+}
+
 Matrix4x4
 AdjustForClip(const Matrix4x4& asyncTransform, Layer* aLayer)
 {
   Matrix4x4 result = asyncTransform;
 
   // Container layers start at the origin, but they are clipped to where they
   // actually have content on the screen. The tree transform is meant to apply
   // to the clipped area. If the tree transform includes a scale component,
@@ -1047,16 +1089,23 @@ AsyncCompositionManager::TransformScroll
   oldTransform.PreScale(underZoomScale.width, underZoomScale.height, 1);
 
   // Make sure fixed position layers don't move away from their anchor points
   // when we're asynchronously panning or zooming
   AlignFixedAndStickyLayers(aLayer, aLayer, metrics.GetScrollId(), oldTransform,
                             aLayer->GetLocalTransform(), fixedLayerMargins);
 }
 
+void
+AsyncCompositionManager::GetFrameUniformity(FrameUniformityData* aOutData)
+{
+  MOZ_ASSERT(CompositorParent::IsInCompositorThread());
+  mFrameUniformityData.EndTest(aOutData);
+}
+
 bool
 AsyncCompositionManager::TransformShadowTree(TimeStamp aCurrentFrame,
                                              TransformsToSkip aSkip)
 {
   PROFILER_LABEL("AsyncCompositionManager", "TransformShadowTree",
     js::ProfileEntry::Category::GRAPHICS);
 
   Layer* root = mLayerManager->GetRoot();
@@ -1099,16 +1148,19 @@ AsyncCompositionManager::TransformShadow
   }
 
   LayerComposite* rootComposite = root->AsLayerComposite();
 
   gfx::Matrix4x4 trans = rootComposite->GetShadowTransform();
   trans *= gfx::Matrix4x4::From2D(mWorldTransform);
   rootComposite->SetShadowTransform(trans);
 
+  if (gfxPrefs::CollectScrollTransforms()) {
+    RecordShadowTransforms(root);
+  }
 
   return wantNextFrame;
 }
 
 void
 AsyncCompositionManager::SetFirstPaintViewport(const LayerIntPoint& aOffset,
                                                const CSSToLayerScale& aZoom,
                                                const CSSRect& aCssPageRect)
diff --git a/gfx/layers/composite/AsyncCompositionManager.h b/gfx/layers/composite/AsyncCompositionManager.h
--- a/gfx/layers/composite/AsyncCompositionManager.h
+++ b/gfx/layers/composite/AsyncCompositionManager.h
@@ -9,26 +9,28 @@
 #include "Units.h"                      // for ScreenPoint, etc
 #include "mozilla/layers/LayerManagerComposite.h"  // for LayerManagerComposite
 #include "mozilla/Attributes.h"         // for final, etc
 #include "mozilla/RefPtr.h"             // for RefCounted
 #include "mozilla/TimeStamp.h"          // for TimeStamp
 #include "mozilla/dom/ScreenOrientation.h"  // for ScreenOrientation
 #include "mozilla/gfx/BasePoint.h"      // for BasePoint
 #include "mozilla/gfx/Matrix.h"         // for Matrix4x4
+#include "mozilla/layers/FrameUniformityData.h" // For FrameUniformityData
 #include "mozilla/layers/LayersMessages.h"  // for TargetConfig
 #include "nsRefPtr.h"                   // for nsRefPtr
 #include "nsISupportsImpl.h"            // for LayerManager::AddRef, etc
 
 namespace mozilla {
 namespace layers {
 
 class AsyncPanZoomController;
 class Layer;
 class LayerManagerComposite;
+class FrameUniformityData;
 class AutoResolveRefLayers;
 
 // Represents (affine) transforms that are calculated from a content view.
 struct ViewTransform {
   explicit ViewTransform(LayerToParentLayerScale aScale = LayerToParentLayerScale(),
                          ParentLayerPoint aTranslation = ParentLayerPoint())
     : mScale(aScale)
     , mTranslation(aTranslation)
@@ -65,29 +67,22 @@ struct ViewTransform {
  * (LayerManagerComposite) which deals with elements of composition which are
  * usually dealt with by dom or layout when main thread rendering, but which can
  * short circuit that stuff to directly affect layers as they are composited,
  * for example, off-main thread animation, async video, async pan/zoom.
  */
 class AsyncCompositionManager final
 {
   friend class AutoResolveRefLayers;
-  ~AsyncCompositionManager()
-  {
-  }
+  ~AsyncCompositionManager();
+
 public:
   NS_INLINE_DECL_REFCOUNTING(AsyncCompositionManager)
 
-  explicit AsyncCompositionManager(LayerManagerComposite* aManager)
-    : mLayerManager(aManager)
-    , mIsFirstPaint(true)
-    , mLayersUpdated(false)
-    , mReadyForCompose(true)
-  {
-  }
+  explicit AsyncCompositionManager(LayerManagerComposite* aManager);
 
   /**
    * This forces the is-first-paint flag to true. This is intended to
    * be called by the widget code when it loses its viewport information
    * (or for whatever reason wants to refresh the viewport information).
    * The information refresh happens because the compositor will call
    * SetFirstPaintViewport on the next frame of composition.
    */
@@ -118,16 +113,23 @@ public:
 
   // True if the underlying layer tree is ready to be composited.
   bool ReadyForCompose() { return mReadyForCompose; }
 
   // Returns true if the next composition will be the first for a
   // particular document.
   bool IsFirstPaint() { return mIsFirstPaint; }
 
+  // After enough calls to RecordShadowTransforms, GetFrameUniformity
+  // will return the frame uniformity for each layer attached to an APZ
+  void GetFrameUniformity(FrameUniformityData* aFrameUniformityData);
+
+  // Records the shadow transform for a given layer due to a scroll
+  void RecordShadowTransforms(Layer* aLayer);
+
 private:
   void TransformScrollableLayer(Layer* aLayer);
   // Return true if an AsyncPanZoomController content transform was
   // applied for |aLayer|.
   bool ApplyAsyncContentTransformToTree(Layer* aLayer);
   /**
    * Update the shadow transform for aLayer assuming that is a scrollbar,
    * so that it stays in sync with the content that is being scrolled by APZ.
@@ -203,16 +205,17 @@ private:
 
   // This flag is set during a layers update, so that the first composition
   // after a layers update has it set. It is cleared after that first composition.
   bool mLayersUpdated;
 
   bool mReadyForCompose;
 
   gfx::Matrix mWorldTransform;
+  FrameUniformityData mFrameUniformityData;
 };
 
 MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(AsyncCompositionManager::TransformsToSkip)
 
 class MOZ_STACK_CLASS AutoResolveRefLayers {
 public:
   explicit AutoResolveRefLayers(AsyncCompositionManager* aManager) : mManager(aManager)
   {
diff --git a/gfx/layers/composite/FrameUniformityData.cpp b/gfx/layers/composite/FrameUniformityData.cpp
new file mode 100644
--- /dev/null
+++ b/gfx/layers/composite/FrameUniformityData.cpp
@@ -0,0 +1,153 @@
+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "FrameUniformityData.h"
+
+#include <map>
+
+#include "gfxPoint.h"
+#include "mozilla/TimeStamp.h"
+#include "nsTArray.h"
+#include "Units.h"                      // for ScreenPoint, etc
+#include "mozilla/dom/APZTestDataBinding.h"
+#include "mozilla/dom/ToJSValue.h"
+
+namespace mozilla {
+namespace layers {
+
+using namespace gfx;
+
+gfx::Point
+LayerTransforms::GetAverage()
+{
+  MOZ_ASSERT(!mTransforms.IsEmpty());
+
+  Point current = mTransforms[0];
+  Point average;
+  size_t length = mTransforms.Length();
+
+  for (size_t i = 1; i < length; i++) {
+    Point nextTransform = mTransforms[i];
+    Point movement = nextTransform - current;
+    average += Point(std::fabs(movement.x), std::fabs(movement.y));
+    current = nextTransform;
+  }
+
+  average = average / (float) length;
+  return average;
+}
+
+gfx::Point
+LayerTransforms::GetStdDev()
+{
+  gfx::Point average = GetAverage();
+  gfx::Point stdDev;
+  gfx::Point current = mTransforms[0];
+
+  for (size_t i = 1; i < mTransforms.Length(); i++) {
+    gfx::Point next = mTransforms[i];
+    gfx::Point move = next - current;
+    move.x = fabs(move.x);
+    move.y = fabs(move.y);
+
+    Point diff = move - average;
+    diff = diff * diff;
+    stdDev += diff;
+
+    current = next;
+  }
+
+  stdDev = stdDev / mTransforms.Length();
+  stdDev.x = sqrt(stdDev.x);
+  stdDev.y = sqrt(stdDev.y);
+  return stdDev;
+}
+
+FrameUniformityData::~FrameUniformityData()
+{
+  Reset();
+}
+
+void
+FrameUniformityData::RecordTransform(Layer* aLayer, const Point aTransform)
+{
+  LayerTransforms* layerTransforms = GetLayerTransforms((uintptr_t) aLayer);
+  layerTransforms->mTransforms.AppendElement(aTransform);
+}
+
+void
+FrameUniformityData::EndTest(FrameUniformityData* aOutData)
+{
+  std::map<uintptr_t, LayerTransforms*>::iterator iter;
+  for (iter = mFrameTransforms.begin(); iter != mFrameTransforms.end(); ++iter) {
+    uintptr_t layer = iter->first;
+    float uniformity = CalculateFrameUniformity(layer);
+
+    std::pair<uintptr_t,float> result(layer, uniformity);
+    aOutData->mUniformities.insert(result);
+  }
+
+  Reset();
+}
+
+LayerTransforms*
+FrameUniformityData::GetLayerTransforms(uintptr_t aLayer)
+{
+  if (!mFrameTransforms.count(aLayer)) {
+    LayerTransforms* newTransform = new LayerTransforms();
+    std::pair<uintptr_t, LayerTransforms*> newLayer(aLayer, newTransform);
+    mFrameTransforms.insert(newLayer);
+  }
+
+  return mFrameTransforms.find(aLayer)->second;
+}
+void
+FrameUniformityData::Reset()
+{
+  std::map<uintptr_t, LayerTransforms*>::iterator iter;
+  for (iter = mFrameTransforms.begin(); iter != mFrameTransforms.end(); ++iter) {
+    LayerTransforms* layerTransforms = iter->second;
+    delete layerTransforms;
+  }
+
+  mFrameTransforms.clear();
+}
+
+float
+FrameUniformityData::CalculateFrameUniformity(uintptr_t aLayer)
+{
+  LayerTransforms* layerTransform = GetLayerTransforms(aLayer);
+  float yUniformity = -1;
+  if (!layerTransform->mTransforms.IsEmpty()) {
+    Point stdDev = layerTransform->GetStdDev();
+    yUniformity = stdDev.y;
+  }
+  return yUniformity;
+}
+
+bool
+FrameUniformityData::ToJS(JS::MutableHandleValue aOutValue, JSContext* aContext)
+{
+  dom::FrameUniformityResults results;
+  dom::Sequence<dom::FrameUniformity>& layers = results.mLayerUniformities.Construct();
+
+  std::map<uintptr_t,float>::iterator iter;
+  for (iter = mUniformities.begin(); iter != mUniformities.end(); ++iter) {
+    uintptr_t layerAddr = iter->first;
+    float uniformity = iter->second;
+
+    layers.AppendElement();
+    dom::FrameUniformity& entry = layers.LastElement();
+
+    entry.mLayerAddress.Construct() = layerAddr;
+    entry.mFrameUniformity.Construct() = uniformity;
+  }
+
+  bool result = dom::ToJSValue(aContext, results, aOutValue);
+  return result;
+}
+
+}
+}
diff --git a/gfx/layers/composite/FrameUniformityData.h b/gfx/layers/composite/FrameUniformityData.h
new file mode 100644
--- /dev/null
+++ b/gfx/layers/composite/FrameUniformityData.h
@@ -0,0 +1,71 @@
+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_layers_FrameUniformityData_h_
+#define mozilla_layers_FrameUniformityData_h_
+
+#include "nsRefPtr.h"
+#include "ipc/IPCMessageUtils.h"
+#include "js/TypeDecls.h"
+
+namespace mozilla {
+namespace layers {
+class Layer;
+
+struct LayerTransforms {
+  LayerTransforms() {}
+
+  gfx::Point GetAverage();
+  gfx::Point GetStdDev();
+
+  // 60 fps * 5 seconds worth of data
+  nsAutoTArray<gfx::Point, 300> mTransforms;
+};
+
+class FrameUniformityData {
+  friend struct IPC::ParamTraits<FrameUniformityData>;
+
+public:
+  FrameUniformityData() {}
+  ~FrameUniformityData();
+
+  void RecordTransform(Layer* aLayer, const gfx::Point aTransform);
+  void Reset();
+  void EndTest(FrameUniformityData* aOutData);
+  bool ToJS(JS::MutableHandleValue aOutValue, JSContext* aContext);
+
+private:
+  float CalculateFrameUniformity(uintptr_t aLayer);
+  LayerTransforms* GetLayerTransforms(uintptr_t aLayer);
+  // Contains a list of all frame transforms
+  std::map<uintptr_t,LayerTransforms*> mFrameTransforms;
+
+  // Contains the calculated frame uniformities
+  std::map<uintptr_t,float> mUniformities;
+};
+
+} // mozilla
+} // layers
+
+namespace IPC {
+template<>
+struct ParamTraits<mozilla::layers::FrameUniformityData>
+{
+  typedef mozilla::layers::FrameUniformityData paramType;
+
+  static void Write(Message* aMsg, const paramType& aParam)
+  {
+    WriteParam(aMsg, aParam.mUniformities);
+  }
+
+  static bool Read(const Message* aMsg, void** aIter, paramType* aResult)
+  {
+    return ParamTraitsStd<std::map<uintptr_t,float>>::Read(aMsg, aIter, &aResult->mUniformities);
+  }
+};
+
+}// ipc
+
+#endif // mozilla_layers_FrameUniformityData_h_
diff --git a/gfx/layers/ipc/CompositorParent.cpp b/gfx/layers/ipc/CompositorParent.cpp
--- a/gfx/layers/ipc/CompositorParent.cpp
+++ b/gfx/layers/ipc/CompositorParent.cpp
@@ -32,16 +32,17 @@
 #include "mozilla/layers/APZCTreeManager.h"  // for APZCTreeManager
 #include "mozilla/layers/APZThreadUtils.h"  // for APZCTreeManager
 #include "mozilla/layers/AsyncCompositionManager.h"
 #include "mozilla/layers/BasicCompositor.h"  // for BasicCompositor
 #include "mozilla/layers/Compositor.h"  // for Compositor
 #include "mozilla/layers/CompositorLRU.h"  // for CompositorLRU
 #include "mozilla/layers/CompositorOGL.h"  // for CompositorOGL
 #include "mozilla/layers/CompositorTypes.h"
+#include "mozilla/layers/FrameUniformityData.h"
 #include "mozilla/layers/LayerManagerComposite.h"
 #include "mozilla/layers/LayersTypes.h"
 #include "mozilla/layers/PLayerTransactionParent.h"
 #include "mozilla/layers/ShadowLayersManager.h" // for ShadowLayersManager
 #include "mozilla/mozalloc.h"           // for operator new, etc
 #include "mozilla/Telemetry.h"
 #ifdef MOZ_WIDGET_GTK
 #include "basic/X11BasicCompositor.h" // for X11BasicCompositor
@@ -1314,16 +1315,23 @@ CompositorParent::ApplyAsyncProperties(L
       CancelCurrentCompositeTask();
       // Pretend we composited in case someone is waiting for this event.
       DidComposite();
     }
   }
 }
 
 bool
+CompositorParent::RecvGetFrameUniformity(FrameUniformityData* aOutData)
+{
+  mCompositionManager->GetFrameUniformity(aOutData);
+  return true;
+}
+
+bool
 CompositorParent::RecvRequestOverfill()
 {
   uint32_t overfillRatio = mCompositor->GetFillRatio();
   unused << SendOverfill(overfillRatio);
   return true;
 }
 
 void
@@ -1700,16 +1708,22 @@ public:
   virtual bool RecvStopFrameTimeRecording(const uint32_t& aStartIndex, InfallibleTArray<float>* intervals) override  { return true; }
   virtual bool RecvGetTileSize(int32_t* aWidth, int32_t* aHeight) override
   {
     *aWidth = gfxPlatform::GetPlatform()->GetTileWidth();
     *aHeight = gfxPlatform::GetPlatform()->GetTileHeight();
     return true;
   }
 
+  virtual bool RecvGetFrameUniformity(FrameUniformityData* aOutData) override
+  {
+    // Don't support calculating frame uniformity on the child process and
+    // this is just a stub for now.
+    return true;
+  }
 
   /**
    * Tells this CompositorParent to send a message when the compositor has received the transaction.
    */
   virtual bool RecvRequestNotifyAfterRemotePaint() override;
 
   virtual PLayerTransactionParent*
     AllocPLayerTransactionParent(const nsTArray<LayersBackend>& aBackendHints,
diff --git a/gfx/layers/ipc/CompositorParent.h b/gfx/layers/ipc/CompositorParent.h
--- a/gfx/layers/ipc/CompositorParent.h
+++ b/gfx/layers/ipc/CompositorParent.h
@@ -224,16 +224,17 @@ public:
                             int aSurfaceWidth = -1, int aSurfaceHeight = -1);
 
   // IToplevelProtocol::CloneToplevel()
   virtual IToplevelProtocol*
   CloneToplevel(const InfallibleTArray<mozilla::ipc::ProtocolFdMapping>& aFds,
                 base::ProcessHandle aPeerProcess,
                 mozilla::ipc::ProtocolCloneContext* aCtx) override;
 
+  virtual bool RecvGetFrameUniformity(FrameUniformityData* aOutData) override;
   virtual bool RecvRequestOverfill() override;
   virtual bool RecvWillStop() override;
   virtual bool RecvStop() override;
   virtual bool RecvPause() override;
   virtual bool RecvResume() override;
   virtual bool RecvNotifyHidden(const uint64_t& id) override { return true; }
   virtual bool RecvNotifyVisible(const uint64_t& id) override { return true; }
   virtual bool RecvNotifyChildCreated(const uint64_t& child) override;
diff --git a/gfx/layers/ipc/PCompositor.ipdl b/gfx/layers/ipc/PCompositor.ipdl
--- a/gfx/layers/ipc/PCompositor.ipdl
+++ b/gfx/layers/ipc/PCompositor.ipdl
@@ -14,16 +14,17 @@ include "nsRegion.h";
 using struct mozilla::null_t from "ipc/IPCMessageUtils.h";
 using struct mozilla::layers::TextureFactoryIdentifier from "mozilla/layers/CompositorTypes.h";
 using struct mozilla::layers::FrameMetrics from "FrameMetrics.h";
 using mozilla::layers::FrameMetrics::ViewID from "FrameMetrics.h";
 using mozilla::layers::LayersBackend from "mozilla/layers/LayersTypes.h";
 using mozilla::CrossProcessMutexHandle from "mozilla/ipc/CrossProcessMutex.h";
 using mozilla::ipc::SharedMemoryBasic::Handle from "mozilla/ipc/SharedMemoryBasic.h";
 using class mozilla::TimeStamp from "mozilla/TimeStamp.h";
+using class mozilla::layers::FrameUniformityData from "mozilla/layers/FrameUniformityData.h";
 
 namespace mozilla {
 namespace layers {
 
 
 /**
  * The PCompositor protocol is used to manage communication between
  * the main thread and the compositor thread context. It's primary
@@ -75,16 +76,19 @@ child:
    * side.
    */
   async ClearCachedResources(uint64_t id);
 
 parent:
   // Child sends the parent a request for fill ratio numbers.
   async RequestOverfill();
 
+  // Child requests frame uniformity measurements
+  sync GetFrameUniformity() returns (FrameUniformityData data);
+
   // The child is about to be destroyed, so perform any necessary cleanup.
   sync WillStop();
 
   // Clean up in preparation for own destruction.
   sync Stop();
 
   // Pause/resume the compositor. These are intended to be used on mobile, when
   // the compositor needs to pause/resume in lockstep with the application.
diff --git a/gfx/layers/moz.build b/gfx/layers/moz.build
--- a/gfx/layers/moz.build
+++ b/gfx/layers/moz.build
@@ -119,16 +119,17 @@ EXPORTS.mozilla.layers += [
     'client/TextureClientPool.h',
     'client/TextureClientRecycleAllocator.h',
     'client/TiledContentClient.h',
     'composite/AsyncCompositionManager.h',
     'composite/CanvasLayerComposite.h',
     'composite/ColorLayerComposite.h',
     'composite/ContainerLayerComposite.h',
     'composite/ContentHost.h',
+    'composite/FrameUniformityData.h',
     'composite/ImageHost.h',
     'composite/ImageLayerComposite.h',
     'composite/LayerManagerComposite.h',
     'composite/PaintedLayerComposite.h',
     'composite/TextureHost.h',
     'Compositor.h',
     'CompositorTypes.h',
     'D3D11ShareHandleImage.h',
@@ -270,16 +271,17 @@ UNIFIED_SOURCES += [
     'client/TiledContentClient.cpp',
     'composite/AsyncCompositionManager.cpp',
     'composite/CanvasLayerComposite.cpp',
     'composite/ColorLayerComposite.cpp',
     'composite/CompositableHost.cpp',
     'composite/ContainerLayerComposite.cpp',
     'composite/ContentHost.cpp',
     'composite/FPSCounter.cpp',
+    'composite/FrameUniformityData.cpp',
     'composite/ImageHost.cpp',
     'composite/ImageLayerComposite.cpp',
     'composite/LayerManagerComposite.cpp',
     'composite/PaintedLayerComposite.cpp',
     'composite/TextRenderer.cpp',
     'composite/TextureHost.cpp',
     'composite/TiledContentHost.cpp',
     'Compositor.cpp',
@@ -384,11 +386,12 @@ CXXFLAGS += [
         'frameworks/base/include/media/stagefright',
         'frameworks/base/include/media/stagefright/openmax',
         'frameworks/av/include/media/stagefright',
         'frameworks/native/include/media/openmax',
     ]
 ]
 
 MOCHITEST_MANIFESTS += ['apz/test/mochitest.ini']
+MOCHITEST_CHROME_MANIFESTS += ['apz/test/chrome.ini']
 
 CXXFLAGS += CONFIG['MOZ_CAIRO_CFLAGS']
 CXXFLAGS += CONFIG['TK_CFLAGS']
diff --git a/gfx/thebes/gfxPrefs.h b/gfx/thebes/gfxPrefs.h
--- a/gfx/thebes/gfxPrefs.h
+++ b/gfx/thebes/gfxPrefs.h
@@ -229,16 +229,17 @@ private:
   DECL_GFX_PREF(Once, "gfx.touch.resample",                    TouchResampling, bool, false);
 
   // These times should be in milliseconds
   DECL_GFX_PREF(Once, "gfx.touch.resample.delay-threshold",    TouchResampleVsyncDelayThreshold, int32_t, 20);
   DECL_GFX_PREF(Once, "gfx.touch.resample.max-predict",        TouchResampleMaxPredict, int32_t, 8);
   DECL_GFX_PREF(Once, "gfx.touch.resample.old-touch-threshold",TouchResampleOldTouchThreshold, int32_t, 17);
   DECL_GFX_PREF(Once, "gfx.touch.resample.vsync-adjust",       TouchVsyncSampleAdjust, int32_t, 5);
 
+  DECL_GFX_PREF(Live, "gfx.vsync.collect-scroll-transforms",   CollectScrollTransforms, bool, false);
   DECL_GFX_PREF(Once, "gfx.vsync.compositor",                  VsyncAlignedCompositor, bool, false);
   // On b2g, in really bad cases, I've seen up to 80 ms delays between touch events and the main thread
   // processing them. So 80 ms / 16 = 5 vsync events. Double it up just to be on the safe side, so 10.
   DECL_GFX_PREF(Once, "gfx.vsync.compositor.unobserve-count",  CompositorUnobserveCount, int32_t, 10);
   // Use vsync events generated by hardware
   DECL_GFX_PREF(Once, "gfx.vsync.hw-vsync.enabled",            HardwareVsyncEnabled, bool, false);
   DECL_GFX_PREF(Once, "gfx.vsync.refreshdriver",               VsyncAlignedRefreshDriver, bool, false);
   DECL_GFX_PREF(Once, "gfx.work-around-driver-bugs",           WorkAroundDriverBugs, bool, true);