Add a test for MediaQueryList::stop().

This CL adds a test for r178732.

BUG=395409
R=haraken@chromium.org

Review URL: https://codereview.chromium.org/404363007

git-svn-id: svn://svn.chromium.org/blink/trunk@178742 bbb929c8-8fbe-4397-9dbb-9b2b20218538