Clean up forward declarations in Source/modules

Source/modules/webdatabase/DatabaseContext.h

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * 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:
  * 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 15 matching lines @@
  */
 
 #ifndef DatabaseContext_h
 #define DatabaseContext_h
 
 #include "core/dom/ActiveDOMObject.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
-class Database;
 class DatabaseContext;
 class TaskSynchronizer;
 class DatabaseThread;
 class ExecutionContext;
 class SecurityOrigin;
 
 class DatabaseContext final
     : public GarbageCollectedFinalized<DatabaseContext>
     , public ActiveDOMObject {
 public:
@@ skipping 25 matching lines @@
     explicit DatabaseContext(ExecutionContext*);
 
     Member<DatabaseThread> m_databaseThread;
     bool m_hasOpenDatabases; // This never changes back to false, even after the database thread is closed.
     bool m_hasRequestedTermination;
 };
 
 } // namespace blink
 
 #endif // DatabaseContext_h