Move read/write-Pixels up to GrSurfaceContext

This still needs to be propagated out in several ways:
  replace more instances of GrSurface::read/write-Pixels
  add colorSpace to more instances of the TextureContext

but it establishes a beach-head and is exciting enough as is.

Change-Id: If86035aa0245e70b54541e83722b3c75bc5ade13
Reviewed-on: https://skia-review.googlesource.com/7172
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
15 files changed