Control making of GrSemaphore objects inside of GrResourceProvider

This change will help us get to the point of not needing access to the GrGpu
object from GrContext.

BUG=skia:

Change-Id: Icff9815c73f1791d2ce34a4d27c57898a36f2b8f
Reviewed-on: https://skia-review.googlesource.com/9391
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
8 files changed