gpudevice should never allocate pixels for its backend

BUG=
R=bsalomon@google.com, mtklein@google.com

Author: reed@google.com

Review URL: https://codereview.chromium.org/109013002

git-svn-id: http://skia.googlecode.com/svn/trunk@12554 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed