Improve modules' TypeError exception messages.

Source/modules/mediastream/RTCPeerConnection.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 486 matching lines @@
 }
 
 PassRefPtr<RTCDTMFSender> RTCPeerConnection::createDTMFSender(PassRefPtr<MediaStreamTrack> prpTrack, ExceptionState& exceptionState)
 {
     if (m_signalingState == SignalingStateClosed) {
         exceptionState.throwUninformativeAndGenericDOMException(InvalidStateError);
         return 0;
     }
 
     if (!prpTrack) {
-        exceptionState.throwUninformativeAndGenericTypeError();
+        exceptionState.throwTypeError("The MediaStreamTrack provided is invalid.");
         return 0;
     }
 
     RefPtr<MediaStreamTrack> track = prpTrack;
 
     if (!hasLocalStreamWithTrackId(track->id())) {
         exceptionState.throwUninformativeAndGenericDOMException(SyntaxError);
         return 0;
     }
 
@@ skipping 168 matching lines @@
     events.swap(m_scheduledEvents);
 
     Vector<RefPtr<Event> >::iterator it = events.begin();
     for (; it != events.end(); ++it)
         dispatchEvent((*it).release());
 
     events.clear();
 }
 
 } // namespace WebCore