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Currently, HitTestAggregator is owned by RootCompositorFrameSinkImpl,
which would only work for the viz display compositor (OOP-D) case. In
non-viz, we use DirectLayerTreeFrameSink, and it calls to create a
CompositorFrameSinkSupport with |is_root| equal to true through
HostFrameSinkManager.

1. This changes CompositorFrameSinkSupport to own the HitTestAggregator
when it is a root CFSS, and pass its FrameSinkId to the HTA.
2. Change FrameSinkManagerImpl to be a HitTestAggregatorDelegate.
3. Update DirectLayerTreeFrameSink to activate HitTestAggregator::
Aggregate().

Bug: 805581
Test: viz_unittests
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel
Change-Id: I0d3d93405dc99e7a5a6edb8f0587c5d0d24ffad7
Reviewed-on: https://chromium-review.googlesource.com/884324
Commit-Queue: Ria Jiang <riajiang@chromium.org>
Reviewed-by: kylechar <kylechar@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534186}