Add explicit UniqueID classes for GrGpuResource & GrSurfaceProxy

This sets the stage for using the Proxy's/RenderTargetContext's ID above the flush and the RenderTarget's/GrGpuResource's below the flush.

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4650

Change-Id: I9f1e6b00c02a0691d90b58c49e1d8c60684884c1
Reviewed-on: https://skia-review.googlesource.com/4650
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
31 files changed