Use the GrCacheable ID to eliminate the need for notifications to GrGpuGL when textures and RTs are deleted. Also, rename GrCacheable::getGenerationID() to getInstanceID() since it doesn't behave like other "generation" IDs. R=jvanverth@google.com Author: bsalomon@google.com Review URL: https://codereview.chromium.org/376703009