Mostly plumbing, plus some minimal testing to make sure that
the platform APIs don't explode. I plan to add testing of
SkCrossContextImageData using this, which should verify that
textures are actually shared.
Also found a factory and some related code in the
CommandBuffer test context that was totally unused.
BUG=skia:
Change-Id: I05bbc22c4d1ef946b702a5cc7f67788785219c62
Reviewed-on: https://skia-review.googlesource.com/8808
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
