compositor-worker: Add CompositorProxyClient worker client of CompositorWorker.

Adds the CompositorProxyClient worker to CompositorWorkers. In order to test
calling animation frame callbacks a task is created to call them when an
animation frame is requested.

BUG=430155
TEST=virtual/threaded/fast/compositorworker/request-animation-frame.html

Review-Url: https://codereview.chromium.org/1956893003
Cr-Commit-Position: refs/heads/master@{#396018}
26 files changed