Reland "[BGPT] Let cc initialize animation states in property nodes"

This is a reland of 54b17c7e812cd7c961abb45b4f8bcc7e2b1bbe43

The original CL called MutatorHost::InitClientAnimationState()
before updating animations. The new CL calls it after updating
animations. Not sure why the original CL caused flakiness of
virtual/threaded/animations/hit-testing/composited-with-hit-testing.html,
but the test is no longer flaky with this new CL.

Original change's description:
> [BGPT] Let cc initialize animation states in property nodes
>
> In this way, blink::PropertyTreeManager no longer needs to care about
> the animation states. Now we initialize and change the states from a
> single source to avoid duplicate code and inconsistency.
>
> Bug: 935770
> Change-Id: I7f98d66677f557213fd4559895e9c2069de196e7
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1513922
> Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
> Reviewed-by: Robert Flack <flackr@chromium.org>
> Reviewed-by: Philip Rogers <pdr@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#640892}

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

Bug: 935770
Change-Id: Icd7ec59b9e5b95f2c268baf88732788cde5da9c6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1525449
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641098}
12 files changed