Move op memory storage to GrContext

TBR=bsalomon@google.com
Change-Id: Ifa95bf0073b9d948f2c937d10088b7734b971f90
Reviewed-on: https://skia-review.googlesource.com/131500
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
40 files changed