Bug 1186956 - 2-20% svgr_opacity/tp5_responsiveness regressions on win* platforms seen on inbound July 21

Revisions (based on 8bae34af92ea):

Fast (profile):

Fast (no profile):

https://treeherder.mozilla.org/#/jobs?repo=try&revision=f8e2f77a0755

Task.async:

https://treeherder.mozilla.org/#/jobs?repo=try&revision=2eaa40679192

GC / CC between pageloads:

https://treeherder.mozilla.org/#/jobs?repo=try&revision=dccc14c00cd2

Add talos-content to xperf whitelist:

https://treeherder.mozilla.org/#/jobs?repo=try&revision=b63e4d781749

Slow:

https://treeherder.mozilla.org/#/jobs?repo=try&revision=ba2e695c2287

Fast: http://people.mozilla.org/~bgirard/cleopatra/?zippedProfile=http://mozilla-releng-blobs.s3.amazonaws.com/blobs/Try/sha512/ad02f7799e6e10c55934df5811ad51cfe10278dbc4825bb5335c1f93b41410aeb87d46a02316951cecc12e921dad42d5c89268efaabca960ba07cb637351906c&pathInZip=profile_tsvgr_opacity/big-optimizable-group-opacity-2500.svg/cycle_0.sps#report=1328ca417cbbfa1610bf63298732457c2830e53e&invertCallback=true&filter=%5B%7B%22type%22%3A%22RangeSampleFilter%22,%22start%22%3A11490,%22end%22%3A45978%7D%5D&selection=%22(total)%22,978

Slow: http://people.mozilla.org/~bgirard/cleopatra/?zippedProfile=http://mozilla-releng-

blobs.s3.amazonaws.com/blobs/Try/sha512/b14681a1d4eca3684b9b964cbed3d3d96e57effc12b4c972e838f64815fd84a406dcce6b027bd3cfd81dcedd64e2d650c1a5fd7ca28be876d19eba554e208d86&pathInZip=profile_tsvgr_opacity/big-optimizable-group-opacity-2500.svg/cycle_0.sps#report=a3d9ad1755860d0d89e24d563bcdea4db2707631&invertCallback=true&filter=%5B%7B%22type%22%3A%22RangeSampleFilter%22,%22start%22%3A11541,%22end%22%3A46556%7D%5D&selection=%22(total)%22,168,168,968,967,966,959,958,957,1057,1056,615,614,613,943,942,941,940,608,939,1055,1054,1053,1052,1051,226,225,224,223,600,599,598,597,596,598,597,596,595,594,593,592,591,226,225,224,223,222,221,220,219,218,217,216,215,214,197,195,194

Fast: http://people.mozilla.org/~bgirard/cleopatra/?zippedProfile=http://mozilla-releng-blobs.s3.amazonaws.com/blobs/Try/sha512/f22118f531323f7938df621de107c24786cb535752fce3e0a6c2f84aefc964ff1068b4b71aeac5d1bd87811d558b4421904141a79afee10dbe254190eb45d3ff&pathInZip=profile_tsvgr_opacity/small-group-opacity-2500.svg/cycle_0.sps#report=2d97614a5ffa73fe4e40003987bb512cdb19385b&invertCallback=true

Slow: http://people.mozilla.org/~bgirard/cleopatra/?zippedProfile=http://mozilla-releng-blobs.s3.amazonaws.com/blobs/Try/sha512/462da30e42d028971c01e57f6fa296abaa30b8524f354e470f1c83cfb8ae1b8fc06bac94d8b20d0c4498b1945b40528c0fdf484b208bccb77e236c007d10cfde&pathInZip=profile_tsvgr_opacity/small-group-opacity-2500.svg/cycle_0.sps#report=bb1727867a09351c9116503d4d7863373356aea4&invertCallback=true&selection=%22(total)%22,98

Remove new Date: https://treeherder.mozilla.org/#/jobs?repo=try&revision=6493a9db4439

Remove garbage collect: https://treeherder.mozilla.org/#/jobs?repo=try&revision=79b6b2b37779

Before (hopefully slow): https://treeherder.mozilla.org/#/jobs?repo=try&revision=467107cda21f

After (hopefully fast): https://treeherder.mozilla.org/#/jobs?repo=try&revision=79af0f0f6897

After with e10s (hopefully unchanged): https://treeherder.mozilla.org/#/jobs?repo=try&revision=5662e518afa9