Remove atlas creation from GrResourceProvider

This is pulled out of: https://skia-review.googlesource.com/c/6680/ (Make SkImage_Gpu be deferred) and is only tangentially related to the goal of that CL.

Change-Id: I6b6db4869597070f85ab3b9fea178fc88c104f87
Reviewed-on: https://skia-review.googlesource.com/9106
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
16 files changed