Add test for slow performance in bug 438509, as suggested by dholbert, and based on a testcase he wrote.
diff --git a/layout/generic/crashtests/438509-1.html b/layout/generic/crashtests/438509-1.html
new file mode 100644
--- /dev/null
+++ b/layout/generic/crashtests/438509-1.html
@@ -0,0 +1,80 @@
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diff --git a/layout/generic/crashtests/crashtests.list b/layout/generic/crashtests/crashtests.list
--- a/layout/generic/crashtests/crashtests.list
+++ b/layout/generic/crashtests/crashtests.list
@@ -150,10 +150,11 @@ load 423055-1.html
load 423055-1.html
load 425253-1.html
load 426272-1.html
load 428263-1.html
load 429981-1.html
load 430352-1.html
load 437156-1.html
load 438259-1.html
+load 438509-1.html
load 448903-1.html
load 451334-1.html