make CT skia_try_server work with updated render_pictures JSON

needed to stay in sync with https://codereview.chromium.org/226293002

BUG=skia:2230
NOTREECHECKS=True
NOTRY=True
R=rmistry@google.com

Author: epoger@google.com

Review URL: https://codereview.chromium.org/227673005
4 files changed