test: add videoElement.loadedmetadata test
test: add videoElement.loadedmetadata test

adds a test which is similar to the web-platform-test simplecall test
  https://github.com/w3c/web-platform-tests/blob/master/webrtc/simplecall.html

Would have probably caught #487.

webrtc/adapter,Acidburn0zzz/adapter,xdumaine/adapter,xdumaine/adapter,Acidburn0zzz/adapter,Acidburn0zzz/adapter,webrtc/adapter,jan-ivar/adapter,jan-ivar/adapter