make onReadPixels protected and have default impl (so we can remove chrome override)

R=reed@google.com
TBR=bsalomon@google.com

Author: reed@chromium.org

Review URL: https://codereview.chromium.org/196543004

git-svn-id: http://skia.googlecode.com/svn/trunk@13756 2bbb7eff-a529-9590-31e7-b0007b416f81
2 files changed