Add a GrContextThreadSafeProxy to SkSurfaceCharacterization

Ganesh will require access to the GrCaps to make rendering decisions.

Change-Id: I6dee42a3f0dc638f052706b8d1ea6e02b589e062
Reviewed-on: https://skia-review.googlesource.com/77681
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
7 files changed