base

Implement SkCanvasGlue::clipRegion() using clipPath().

(Canvas clipRegion() public API is scheduled for deprecation)

The SkCanvas clip stack does not support clipRegion() ops. Implementing
these in terms of clipPath() makes persisting clips for SaveFlags
emulation purposes a whole lot simpler.

Change-Id: I41d1eb9e292ce370fba224338f9071d5e4068621