Add support to dump font cache texture for debug purposes

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

Author: jvanverth@google.com

Review URL: https://codereview.chromium.org/25736002

git-svn-id: http://skia.googlecode.com/svn/trunk/src@11579 2bbb7eff-a529-9590-31e7-b0007b416f81
5 files changed