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In the situation of there being damage above an overlay we currently do
not remove the damage of the underlay. A good example of where this
occurs is the timeline controls on top of a youtube video. So instead of
doing the smallest amount of damage (say for the seconds counter) we
damage the entire video display region. There are other contexts for
which the overlay damage region is not removed but in the end these all
come down to the difficulty of subtracting damage from the incoming root
damage.

In this change we move from subtracting overlay damage to excluding it
via the |SurfaceDamageList|. This results in much more accurate final
damage and thus improve power usage. This change also dramatically
reduces the complexity of previously error prone overlay damage
subtraction computations.

Finally, this change moves us closer to our goal of doing damage
extraction on a per quad level in surface aggregator.
See this document for more information:
 https://docs.google.com/document/d/
1yDnz1DKcSwfMZwmeRR_RRS3QznpzqLnsMeeYIk-ORfA/edit?usp=sharing



Change-Id: Ia5901546bd3982b8054b5ae9d0f397c22d7e5228
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2558918Reviewed-by: Maggie Chen <magchen@chromium.org>
Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
Commit-Queue: Peter McNeeley <petermcneeley@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836164}