Mark fast/js/const.html for rebaseline, and fix illegal javascript in rubberband test

TBR=pfeldman@chromium.org
BUG=

Review URL: https://codereview.chromium.org/224833006

git-svn-id: svn://svn.chromium.org/blink/trunk@170836 bbb929c8-8fbe-4397-9dbb-9b2b20218538