Move GrDrawingManager pointer to GrSurfaceContext

Change-Id: Ic285b24b384bbf284cc680fe770433dd4d643833
Reviewed-on: https://skia-review.googlesource.com/7561
Reviewed-by: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
7 files changed