Use ct-test-result rather than manually creating an iframe

R=ojan@chromium.org
BUG=387412
NOTRY=true

Review URL: https://codereview.chromium.org/344253012

git-svn-id: svn://svn.chromium.org/blink/trunk@176817 bbb929c8-8fbe-4397-9dbb-9b2b20218538