Expand SkImage::getTextureHandle call

Expand SkImage::getTextureHandle call

AFAICT cc/output/gl_renderer.cc only calls SkImage:getTexture to determine the origin of the backing GrTexture. What do y'all think of this CL as a means of removing that call to getTexture?

One alternative would be to add a new entry point like:

bool SkImage::getBackendTextureDesc(GrBackendTextureDesc* desc) const;

which fills in the entire desc and returns whether the image is texture backed.

Change-Id: Idd302c0a11d69ad08e0100bcf546b3bbaa7cf27e
Reviewed-on: https://skia-review.googlesource.com/7788
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>