Revert "Repaint when bgcolor animation is triggered"

This reverts commit bbf753e8c7ec7c492f4436c2bdee81278309c4d2.

Reason for revert: Too much flakiness in blink_web_tests on Linux*

Recent failures:
- https://ci.chromium.org/p/chromium/builders/ci/Linux%20Tests/98274
- https://ci.chromium.org/p/chromium/builders/ci/linux-bfcache-rel/15065
- https://ci.chromium.org/p/chromium/builders/ci/linux-trusty-rel/21522

Original change's description:
> Repaint when bgcolor animation is triggered
>
> Right now when a bgcolor animation/transition is triggered, such
> as hovering over an element, we do not request a repaint of the
> element and thus we cannot composite the bgcolor animation.
>
> This CL fixes the problem by triggering a full repaint.
>
> Bug: 1177320
> Change-Id: I87dff5c11d109fc97f41c9b49e13b81613004281
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2698847
> Reviewed-by: Philip Rogers <pdr@chromium.org>
> Reviewed-by: Robert Flack <flackr@chromium.org>
> Commit-Queue: Xida Chen <xidachen@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#857877}

Bug: 1177320
Change-Id: Ifabf8f703af522a6ea25aeac3e76926478a01610
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2719692
Reviewed-by: Jiewei Qian  <qjw@chromium.org>
Auto-Submit: Jiewei Qian  <qjw@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#857947}