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Prior to this CL, an impl-side child allocated LocalSurfaceId would cause
a spurious commit on the main thread as the new LocalSurfaceId propagates its
way back to the main thread from the parent renderer.

LayerTreeHost::SetLocalSurfaceIdFromParent really only cares about changes
to the parent_sequence_number and embed_token to propagate to the impl thread.
Other changes are irrelevant and should not cause commits.

This CL fixes the issue by early exiting in
LayerTreeHost::SetLocalSurfaceIdFromParent. This problem was cause by looking
at SurfaceId flows. This will likely improve scrolling performance a bit on
Android.

Bug: 672962
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ide4f9df9d89c70216e9a54dfc6ccd298cf046821
Reviewed-on: https://chromium-review.googlesource.com/1126325Reviewed-by: Saman Sami <samans@chromium.org>
Commit-Queue: Fady Samuel <fsamuel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572622}