add explicit filepaths to render_pictures JSON summary

BUG=skia:2230,skia:1942
R=rmistry@google.com

Author: epoger@google.com

Review URL: https://codereview.chromium.org/226293002

git-svn-id: http://skia.googlecode.com/svn/trunk@14133 2bbb7eff-a529-9590-31e7-b0007b416f81
7 files changed