add SkImageInfo to SkGrPixelRef constructor, to prep for larger CL

BUG=

Review URL: https://codereview.chromium.org/104923011

git-svn-id: http://skia.googlecode.com/svn/trunk@12559 2bbb7eff-a529-9590-31e7-b0007b416f81
2 files changed