Use [TypeChecking=Unrestricted] for HTMLMediaElement

BUG=354298
TBR=acolwell

Review URL: https://codereview.chromium.org/261783009

git-svn-id: svn://svn.chromium.org/blink/trunk@173150 bbb929c8-8fbe-4397-9dbb-9b2b20218538