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I had this CL that implements animation specific UMA:
https://chromium-review.googlesource.com/c/chromium/src/+/636305
In particular, we record frame rate when there is main thread / compositor /
main thread compositable animations in this frame. However, the main
thread compositable animations is not calculated correctly in the above
CL. The result of that is a crash which is tracked in crbug.com/781305.
In order to solve the crash, we temporary disabled the main thread
compositable animation UMA in here:
https://chromium-review.googlesource.com/c/chromium/src/+/753405

Now it is time to re-enable that UMA. This is how we check whether an
animation is main thread compositable or not: we first check whether the
effects can start on compositor or not. For example, a transform animation
will be able to start on compositor. Then we check whether the target
element can start on compositor or not. If the target element is not
paint into its own backing, we know that this is due to a running
experiment.

The problem with the above logic is SVG element. For example, if we
have a transform animation on an SVG element, the effect can be started
on compositor but the SVG element cannot start on compositor. In order
to tell whether this is a main thread compositable, we have to exclude
the SVG element.

This CL fixed the problem. It re-enables a unit test and added another
test for SVG element.

Bug: 781305
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I030f2e7d2061589ccb0a62f12744b1097855f2f7
Reviewed-on: https://chromium-review.googlesource.com/895409Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Commit-Queue: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534820}