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This allows a bunch of code to be deleted as well.

Need to fix up unit tests which was still using synchronous draw, and
thus having wrong expectations.

Change-Id: Ia5504545f213bf709951eb2213dc40aaca4fc6be
Reviewed-on: https://chromium-review.googlesource.com/949085
Commit-Queue: Bo <boliu@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Tobias Sargeant <tobiasjs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#541729}