Add checks that the GrResourceAllocator is operating as expected

With explicit resource allocation there should be no explicit instantiating at flush time. There are, however, still several instances where instantiate is called outside of testing (e.g., readSurfacePixels and writeSurfacePixels).

Change-Id: Ic459a550ca85048f66d6a1eb7d601411f83c6e32
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/204721
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
16 files changed