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This change routes HitTestRegionList objects received by
CompositorFrameSinkSupport to the HitTestManager.

The HitTestAggregator will query the HitTestManager for the
active HitTestRegionLists when aggregating the data.

HitTestManager also manages the lifetime of HitTestRegionList
objects by deleting old objects when surfaces are discarded
and deleting objects that correspond to older frames when
a new surface is activated.

This change also modifies HitTestAggregator memory management
so that new memory is allocated as needed while aggregating
HitTestRegionList data.

Bug: 732399
Change-Id: Iaedec31a34f04446a539acd10d77c6fe18034d44
Reviewed-on: https://chromium-review.googlesource.com/650220
Commit-Queue: Gary Klassen <gklassen@chromium.org>
Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
Reviewed-by: Ria Jiang <riajiang@chromium.org>
Reviewed-by: Fady Samuel <fsamuel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#506780}