Beginning of support for texture rectangles.

Adds support for importing a RECTANGLE texture into Skia via GrTexureProvider::wrapBackendTexture().

Tests read/writing pixels, copySurface, and clear.

Does not add support for texturing from a RECTANGLE texture as the coords will be incorrectly normalized.

BUG=skia:3868
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1583863002

Review URL: https://codereview.chromium.org/1583863002
15 files changed