Add tests to ensure we fire DOM events when a media query changes.

Forgot to add these in https://codereview.chromium.org/396283004

BUG=375658
R=esprehn@chromium.org,yoav@yoav.ws

Review URL: https://codereview.chromium.org/521083002

git-svn-id: svn://svn.chromium.org/blink/trunk@181277 bbb929c8-8fbe-4397-9dbb-9b2b20218538