expose CGImage -> SkBitmap

BUG=skia:
R=scroggo@google.com, halcanary@google.com

Author: reed@google.com

Review URL: https://codereview.chromium.org/243463005

git-svn-id: http://skia.googlecode.com/svn/trunk@14315 2bbb7eff-a529-9590-31e7-b0007b416f81
5 files changed