[Chromium] callOnMainThread should equate to MessageLoop::PostTask
Presently, callOnMainThread is implemented using an intermediate queue, and MessageLoop::PostTask is used to process that queue in batches. This adds ordering problems which cause flaky behavior in Chrome as callOnMainThread and MessageLoop::PostTask are not necessarily FIFO. It is also a potential source of jank as while we are processing the queue, we do not let other tasks run on the thread. It would be better to let the MessageLoop be the scheduler for all callbacks to the main thread.
Chromium bug is here:
Chromium-side pre-req patch is here:
Created attachment 54591 [details]
Landed as http://trac.webkit.org/changeset/58425