[BlinkGenPropertyTrees] Fix ElementIsAnimatingChanged logic

As of https://crrev.com/2a64f7b5, there is no longer a single ElementId
for an entire 'animating target' in cc. However ElementIsAnimatingChanged
still assumes that it can lookup the different types of nodes
(TransformNode, EffectNode) using a single ElementId. This caused both
incorrect logic (code that should have been executed was not as the node
could not be found) as well as DCHECK failures (again from the incorrect

This fix is essentially a hack, and it is important to note that we don't
have a clear idea of what ElementIsAnimatingChanged is required for (i.e.
what the consequences of it not working -outside of DCHECKs - are). The
goal of this CL is just to restore the function to how it was working
before https://crrev.com/2a64f7b5.

Cq-Include-Trybots: luci.chromium.try:linux-blink-gen-property-trees;luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel

Change-Id: I0d0eb0c9add83ff3c1b6d6f30858804aed300aac
Bug: 912574
Reviewed-on: https://chromium-review.googlesource.com/c/1372173
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Reviewed-by: Majid Valipour <majidvp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621198}
14 files changed