Reland "[BlinkGenPropertyTrees] Fix ElementIsAnimatingChanged logic"

This relands the commit b0eab4a3e36612417196e6766d7a770f675169c4 from
https://chromium-review.googlesource.com/c/chromium/src/+/1372173

The only change is to mark virtual/threaded/animations/skew-notsequential-compositor.html
as flaky; it has been decided that it is worth landing the CL anyway
and investigating the flakiness afterwards.

TBR=majidvp@chromium.org,pdr@chromium.org

Bug: 912574, 921105
Change-Id: I93dfc5db4056e3567f99254f28b1072a66c4f532
Reviewed-on: https://chromium-review.googlesource.com/c/1407385
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622123}
14 files changed