Modify content::RunAllTasksUntilIdle() To Use FlushAsyncForTesting()

This allows RunAllTasksUntilIdle() to pump messages and flush at the
same time instead of as separate steps.

BUG=804930

Change-Id: Ie07f320b558abc975f5922e89de33a66f00a48b9
Reviewed-on: https://chromium-review.googlesource.com/884503
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Commit-Queue: Robert Liao <robliao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#535749}
2 files changed