Revise system for checking for uninstantiated proxies

The new pattern is:
  we will "instantiate" pipelines at flush time
  at flush time we will only access the backing GrSurface by peeking

  If instantiation fails we should never try to access the GrSurfaces


Change-Id: I87f7ff41bd0e84d9ca3dbdd61d3361d3d4ceefd6
Reviewed-on: https://skia-review.googlesource.com/17932
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
30 files changed