Fix windows build break.

git-svn-id: http://libjingle.googlecode.com/svn/trunk@111 dd674b97-3498-5ee5-1854-bdd07cd0ff33
diff --git a/talk/session/phone/mediamessages.h b/talk/session/phone/mediamessages.h
index 8a8a6de..6f38a64 100644
--- a/talk/session/phone/mediamessages.h
+++ b/talk/session/phone/mediamessages.h
@@ -45,7 +45,7 @@
 
 namespace cricket {
 
-class StreamParams;
+struct StreamParams;
 
 // A collection of audio and video streams. Most of the methods are
 // merely for convenience. Many of these methods are keyed by ssrc,