chartjson results if available and add a chartjson result to the results
json when present.

I need these results in the chromium_tests SwarmingIsolatedScript class so
that I can upload results to the perf dashboard after a successful swarming
task.  I am not completely replacing the json with chartjson instead of
just json becuase I am not sure if the json form is still needed yet.  This
will be an iterative approach while I try and get a successful swarmed
bencmark on the waterfall.

BUG=chromium:633253

Review-Url: https://codereview.chromium.org/2331993003
Cr-Commit-Position: refs/heads/master@{#419740}