Remove asTextureRef from SkSpecialImage & update effects accordingly

This CL also renames SkSpecialImage::asTextureProxy to asTextureProxyRef

Change-Id: I5ed8e475bb9688453b825ae4500ed0e8d324b5ac
Reviewed-on: https://skia-review.googlesource.com/7995
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
18 files changed