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Start the sampling profiler on the oop-d thread. Plumb the task-runner
of the compositor thread from viz through content to chrome, which
starts the profiler on the thread.

BUG=788808

Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel
Change-Id: Id9e05bc290205ad2d397028313b6e1a2430a9d92
Reviewed-on: https://chromium-review.googlesource.com/943401Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Mike Wittman <wittman@chromium.org>
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#540396}