cc: Remove WebCore rect use from the compositor, except within Region.

cc: Remove WebCore rect use from the compositor, except within Region.

This replaces the last cases of FloatRect with gfx::RectF. It depends on the 
IsExpressibleAsRect() method in https://codereview.chromium.org/11364054/ and 
removes the stubs as well! 

We add an API to the Region class that is intended to be our final Region
class interface. It uses an iterator to walk the rects in the Region, which is
compatible with the SkRegion API, but can also hide the IntRects exposed by the
WebCore Region API.

Once this is done, there is no need to use cc::IntRect, and we can remove it
entirely.

Covered by existing tests; no change in behaviour.

BUG=147395
R=enne

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=165837

[danakj, 2012-11-02 20:16:41]

A potential combination of http://codereview.chromium.org/11369051/ and
https://codereview.chromium.org/11361072/

[enne (OOO), 2012-11-02 21:05:01]

Rubber stamp lgtm

[commit-bot: I haz the power, 2012-11-02 21:50:38]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/danakj@chromium.org/11360066/8001

[commit-bot: I haz the power, 2012-11-03 00:51:39]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/danakj@chromium.org/11360066/8001