Rename GrTextureBufferSampler to GrBufferSampler Just a simple renaming to reinforce the Ganesh notion that a buffer access is not related to a texture. BUG=skia: GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4879 Change-Id: I3f12b6eccff744e246618be0a7abf41c4a1228a1 Reviewed-on: https://skia-review.googlesource.com/4879 Reviewed-by: Brian Salomon <bsalomon@google.com> Commit-Queue: Chris Dalton <csmartdalton@google.com>