Support multiple PDF rendering backends in the GM

R=epoger@google.com, vandebo@chromium.org

Review URL: https://codereview.chromium.org/21669004

git-svn-id: http://skia.googlecode.com/svn/trunk@10841 2bbb7eff-a529-9590-31e7-b0007b416f81
11 files changed