Allow GrSurfaceProxy-derived classes to use flags when instantiating

In some instances proxies must be created that, when instantiated, have no pending IO.

This is split out of: (Add per-Flush callback to GrDrawingManager)

https://skia-review.googlesource.com/c/8679/

Change-Id: I68b5504d35ad436a4ae737ac4bb3c171fc9a5826
Reviewed-on: https://skia-review.googlesource.com/8988
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
12 files changed