make compare_rendered_pictures process render_pictures's new JSON output format

BUG=skia:1942,skia:2230
NOTRY=True
R=borenet@google.com

Author: epoger@google.com

Review URL: https://codereview.chromium.org/265793013

git-svn-id: http://skia.googlecode.com/svn/trunk@14591 2bbb7eff-a529-9590-31e7-b0007b416f81
8 files changed