Add gm that tests shaded stroked rectangles.

Fix GPU handling of previously untested cases.

Move rect->path fallback from SkGpuDevice to GrDrawContext.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2125663003

Review-Url: https://codereview.chromium.org/2125663003
10 files changed