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This aligns animations with virtual time progression when
the CompositorController is used to issue BeginFrames.

Also updates VirtualTimeController to use TimeDeltas instead
of millisecond ints and initializes BeginFrameArgs frame_time
to its minimum value by default to support emulated negative
base::TimeTicks values in continuity DCHECKS throughout the
compositor code.

Bug: 646774
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel
Change-Id: Ia28ab131dd1a327907f8570a1f26ce794208d3d4
Reviewed-on: https://chromium-review.googlesource.com/790910
Commit-Queue: Eric Seckler <eseckler@chromium.org>
Reviewed-by: Alex Clarke <alexclarke@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#519725}