Add drawRegion() API to SkCanvas

This will allow us to optimize for the RectGrid macrobench.
Currently, SkiaGL is much slower than OpenGL.
SkiaGL  12 items/s
OpenGL 160 items/s

This contains everything except for the fast implementation on GPU.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2277053002

Review-Url: https://codereview.chromium.org/2277053002
diff --git a/src/core/SkLiteDL.h b/src/core/SkLiteDL.h
index 4f28486..1549576 100644
--- a/src/core/SkLiteDL.h
+++ b/src/core/SkLiteDL.h
@@ -40,6 +40,7 @@
     void drawPaint (const SkPaint&);
     void drawPath  (const SkPath&, const SkPaint&);
     void drawRect  (const SkRect&, const SkPaint&);
+    void drawRegion(const SkRegion&, const SkPaint&);
     void drawOval  (const SkRect&, const SkPaint&);
     void drawArc   (const SkRect&, SkScalar, SkScalar, bool, const SkPaint&);
     void drawRRect (const SkRRect&, const SkPaint&);