GTTF: report results of all test iterations, to stdout and optionally JSON file.

BUG=236893
R=sky@chromium.org

Review URL: https://codereview.chromium.org/27017006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228488 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228488