Add GMs for testing drawArc.

This is in preparation for virtualizing this on SkCanvas/SkDevice.

Tests the following variations:

aa and non-aa
stroke/hairline/fill
cap types
using center point and not

BUG=skia:5227
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2264593002

Review-Url: https://codereview.chromium.org/2264593002
1 file changed