Move op memory storage to GrContext (take 2)

TBR=bsalomon@google.com

Change-Id: I4a448694d4114d83cd3a720cfc8bd37de51733d1
Reviewed-on: https://skia-review.googlesource.com/135707
Reviewed-by: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
41 files changed