Remove unused Dictionary forward declaration and include

Source/core/dom/MutationObserver.h

 /*
  * Copyright (C) 2011 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 24 matching lines @@
 #include "platform/heap/Handle.h"
 #include "wtf/HashSet.h"
 #include "wtf/PassOwnPtr.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefCounted.h"
 #include "wtf/RefPtr.h"
 #include "wtf/Vector.h"
 
 namespace blink {
 
-class Dictionary;
 class ExceptionState;
 class MutationCallback;
 class MutationObserver;
 class MutationObserverInit;
 class MutationObserverRegistration;
 class MutationRecord;
 class Node;
 
 typedef unsigned char MutationObserverOptions;
 typedef unsigned char MutationRecordDeliveryOptions;
@@ skipping 51 matching lines @@
 
     OwnPtr<MutationCallback> m_callback;
     MutationRecordVector m_records;
     MutationObserverRegistrationSet m_registrations;
     unsigned m_priority;
 };
 
 } // namespace blink
 
 #endif // MutationObserver_h