Set MediaStream CanFireEvent slot to true

Author: youennf

Diff for: webrtc.html

@@ -16540,6 +16540,7 @@ <h4>
             When a {{MediaStream}} is created to represent a stream obtained
             from a remote peer, the {{MediaStream/id}} attribute is initialized
             from information provided by the remote source.
+            The {{MediaStream}}'s [[\CanFireEvent]] slot is set to <code>true</code>.
           </p>
           <p class="note">
             The {{MediaStream/id}} of a {{MediaStream}} object is unique to the