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/SkPictureRecord.h b/src/core/SkPictureRecord.h
index 5601d2a..ac8058b 100644
--- a/src/core/SkPictureRecord.h
+++ b/src/core/SkPictureRecord.h
@@ -186,6 +186,7 @@
     void onDrawPaint(const SkPaint&) override;
     void onDrawPoints(PointMode, size_t count, const SkPoint pts[], const SkPaint&) override;
     void onDrawRect(const SkRect&, const SkPaint&) override;
+    void onDrawRegion(const SkRegion&, const SkPaint&) override;
     void onDrawOval(const SkRect&, const SkPaint&) override;
     void onDrawArc(const SkRect&, SkScalar, SkScalar, bool, const SkPaint&) override;
     void onDrawRRect(const SkRRect&, const SkPaint&) override;