Updating WebM canPlayType Layout Tests to check VP9

Updating the Layout Tests for WebM canPlayType to make sure vp9
returns "probably"

Review URL: https://codereview.chromium.org/69453002

git-svn-id: svn://svn.chromium.org/blink/trunk@161934 bbb929c8-8fbe-4397-9dbb-9b2b20218538