Start on supporting transfer from GrSurface.

This only implements the GrGpu level functionality and is not exposed in
the public API.

Currently implemented for OpenGL only.

Bug: skia:8962

Change-Id: I8e58c1860185aa913bcdb0954908ce9e0b8e78f3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/206383
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
13 files changed