Adding error checks to SkRBuffer

BUG=
R=robertphillips@google.com, bsalomon@google.com, reed@google.com

Author: sugoi@chromium.org

Review URL: https://codereview.chromium.org/61913002

git-svn-id: http://skia.googlecode.com/svn/trunk/src@12202 2bbb7eff-a529-9590-31e7-b0007b416f81
9 files changed