Revert of ui: Clean up damaged rects and clear them after painting. (patchset #2...

Revert of ui: Clean up damaged rects and clear them after painting. (patchset #2 id:20001 of https://codereview.chromium.org/1080633009/)

Reason for revert:
ash_unittests are timing out on Win8 Aura and Linux ChromiumOS Tests (dbg)(1) bot and this CL is suspected to be the cause of the problem.

Original issue's description:
> ui: Clean up damaged rects and clear them after painting.
>
> This cleans up some of the damage rects code by converting the SkRegion
> to a cc::Region, allowing use of gfx::Rects. It moves the recursion
> over the Layer tree out to Compositor instead of on Layer.
>
> And we keep the damaged_region_ valid until the layer is painted. This
> will allow us to pass that damaged_region_ to the painting code with
> impl-side slimming paint, because with impl-side painting, the paint
> clip rect can be larger than the invalidations (as large as the whole
> layer).
>
> R=piman@chromium.org, sky
> BUG=466426
>
> Committed: https://crrev.com/a5e585868e16ce53c990f764d4943592f11749aa
> Cr-Commit-Position: refs/heads/master@{#326547}

TBR=piman@chromium.org,sky@chromium.org,danakj@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=466426

Review URL: https://codereview.chromium.org/1101103004

Cr-Commit-Position: refs/heads/master@{#326637}