Export BindingSecurity checks via WebFrame

      This will allow for leaking cross-context references from extensions

BUG=504011
R=haraken@chromium.org

Review URL: https://codereview.chromium.org/1235463006

git-svn-id: svn://svn.chromium.org/blink/trunk@198774 bbb929c8-8fbe-4397-9dbb-9b2b20218538