make info real in SkPixelRef, and add bitmap::asImageInfo

BUG=
R=scroggo@google.com

Review URL: https://codereview.chromium.org/108663004

git-svn-id: http://skia.googlecode.com/svn/trunk@12586 2bbb7eff-a529-9590-31e7-b0007b416f81
10 files changed