Make blur utils take GrTextureProxies - take 2

This is a re-land of https://skia-review.googlesource.com/c/7738/ (Make blur utils take GrTextureProxies) with a fix for the Nexus7

Change-Id: I5821a26b1e986daa11d960ae826a1207512cd2a0
Reviewed-on: https://skia-review.googlesource.com/7746
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
9 files changed