Add method to iterate over a GrOp's GrSurfaceProxies

The extra generality of having a std::function is for MDB reordering. In the current MDB reordering world there is one pass through the surfaceProxies at creation time and a second pass after flush to create the usage intervals.

Change-Id: I3f548417eddc1dad7503d919241301e404255ffe
Reviewed-on: https://skia-review.googlesource.com/46200
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
30 files changed