Clean up forward declarations in Source/modules

Source/modules/encryptedmedia/MediaKeys.h

 /*
  * Copyright (C) 2013 Apple 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 11 matching lines @@
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
  * THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef MediaKeys_h
 #define MediaKeys_h
 
 #include "bindings/core/v8/ScriptPromise.h"
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "core/dom/ContextLifecycleObserver.h"
-#include "wtf/Forward.h"
-#include "wtf/text/WTFString.h"
 
 namespace blink {
 
-class ExceptionState;
 class ExecutionContext;
-class HTMLMediaElement;
 class MediaKeySession;
 class ScriptState;
 class WebContentDecryptionModule;
 
 // References are held by JS and HTMLMediaElement.
 // The WebContentDecryptionModule has the same lifetime as this object.
 class MediaKeys : public GarbageCollectedFinalized<MediaKeys>, public ContextLifecycleObserver, public ScriptWrappable {
     DEFINE_WRAPPERTYPEINFO();
 public:
     static ScriptPromise create(ScriptState*, const String& keySystem);
@@ skipping 16 matching lines @@
     friend class MediaKeysInitializer;
     MediaKeys(ExecutionContext*, const String& keySystem, PassOwnPtr<blink::WebContentDecryptionModule>);
 
     const String m_keySystem;
     OwnPtr<blink::WebContentDecryptionModule> m_cdm;
 };
 
 } // namespace blink
 
 #endif // MediaKeys_h