Move copy operation from GrRenderTargetContext/GrTextureContext to GrSurfaceContext

Change-Id: I5f48ce9978370f07238a7318ccb6270e10069c92
Reviewed-on: https://skia-review.googlesource.com/21104
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
11 files changed