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Extend Display::RemoveOverdrawQuads to track up to 10 occluding rects as a
region in target space.

cc::Region::GetRegionComplexity() exposes the number of rects
contributing to a region. In the past, using regions as occluders
without limiting the  number of rects contributing to a region resulted
in cases with significant CPU times.

RemoveOverdrawQuadPerfTest benchmark results show little difference
among kMaximumOccluderComplexity values when compared to pre-change
results.

See Occlusion Culling Improvements doc [1] for results details.

[1] https://docs.google.com/document/d/1LeBa-f80FG4eioHpX706Th65FEoXcEzWmNgooZQyNSw/edit?usp=sharing#heading=h.dgeynqo2z2ly

Test: viz_perftests
Bug: 1022544
Change-Id: I1c844490fe57146d9448bcf408ee23dd627657ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2040201
Commit-Queue: Sasha McIntosh <sashamcintosh@chromium.org>
Reviewed-by: Khushal <khushalsagar@chromium.org>
Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Cr-Commit-Position: refs/heads/master@{#740476}