Rewrite inspector/timeline/timeline-frames.html to use actual frame signals

The older implementation used mocked signals that relied on old instrumentation
and non-threaded compositing, thus not adding much to the coverage.
This changes to actually producing frames using rAFs and displayAsyncThen(),
though for virtual/implsidepainting only, as content_shell presently uses
custom code path for compositing in DRT mode.

BUG=405460

Review URL: https://codereview.chromium.org/481513003

git-svn-id: svn://svn.chromium.org/blink/trunk@180651 bbb929c8-8fbe-4397-9dbb-9b2b20218538