UI Compositor: Fix threaded animation survival if layer removed and added.

This is minimal fix, scoped in ui/compositor. To be merged.

In general, we must allow to move AnimationPlayers between timelines inside same Compositor(AnimationHost) without any animation losses.

See http://crbug.com/592873 (To be designed separately)

BUG=591474

Review URL: https://codereview.chromium.org/1776513002

Cr-Commit-Position: refs/heads/master@{#380047}
3 files changed