compositor-worker: Initialize CW machinery plumbing to compositor and fire CW rAF callbacks.

BUG=430155
TEST=virtual/threaded/fast/compositorworker/request-animation-frame.html
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review-Url: https://codereview.chromium.org/1895873006
Cr-Commit-Position: refs/heads/master@{#396829}
43 files changed