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
18 files changed