Fix tile bitmap code in SkGpuDevice to compute correct local coords.

This fixes a bug when using an alpha bitmap/image with a SkShader where the SkShader's GrFragmentProcessor would receive incorrect coordinates.

BUG=skia:5643

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2249163004

Review-Url: https://codereview.chromium.org/2249163004
2 files changed