Clean up forward declarations in Source/modules

Source/modules/encryptedmedia/MediaKeysClient.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MediaKeysClient_h
 #define MediaKeysClient_h
 
 #include "wtf/PassOwnPtr.h"
 #include "wtf/text/WTFString.h"
 
 namespace blink {
 
 class ExecutionContext;
-class Page;
 class WebContentDecryptionModule;
 
 class MediaKeysClient {
 public:
     virtual PassOwnPtr<WebContentDecryptionModule> createContentDecryptionModule(ExecutionContext*, const String& keySystem) = 0;
 
 protected:
     virtual ~MediaKeysClient() { }
 };
 
 } // namespace blink
 
 #endif // MediaKeysClient_h