Remove manual ref()-deref() in DatabaseContext.

Source/modules/webdatabase/DatabaseManager.h

 /*
  * Copyright (C) 2012 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 63 matching lines @@
     PassRefPtrWillBeRawPtr<DatabaseSync> openDatabaseSync(ExecutionContext*, const String& name, const String& expectedVersion, const String& displayName, unsigned long estimatedSize, PassOwnPtr<DatabaseCallback>, DatabaseError&, String& errorMessage);
 
     String fullPathForDatabase(SecurityOrigin*, const String& name, bool createIfDoesNotExist = true);
 
     void closeDatabasesImmediately(const String& originIdentifier, const String& name);
 
     void interruptAllDatabasesForContext(DatabaseContext*);
 
 private:
     DatabaseManager();
-    ~DatabaseManager() { }
+    ~DatabaseManager();
 
     // This gets a DatabaseContext for the specified ExecutionContext.
     // If one doesn't already exist, it will create a new one.
     DatabaseContext* databaseContextFor(ExecutionContext*);
     // This gets a DatabaseContext for the specified ExecutionContext if
     // it already exist previously. Otherwise, it returns 0.
     DatabaseContext* existingDatabaseContextFor(ExecutionContext*);
 
     PassRefPtrWillBeRawPtr<DatabaseBackendBase> openDatabaseBackend(ExecutionContext*,
         DatabaseType, const String& name, const String& expectedVersion, const String& displayName,
         unsigned long estimatedSize, bool setVersionInNewDatabase, DatabaseError&, String& errorMessage);
 
     static void logErrorMessage(ExecutionContext*, const String& message);
 
     AbstractDatabaseServer* m_server;
 
     // Access to the following fields require locking m_contextMapLock:
-    typedef HashMap<ExecutionContext*, DatabaseContext*> ContextMap;
+    typedef HashMap<ExecutionContext*, RefPtr<DatabaseContext> > ContextMap;
     ContextMap m_contextMap;
 #if !ASSERT_DISABLED
     int m_databaseContextRegisteredCount;
     int m_databaseContextInstanceCount;
 #endif
     Mutex m_contextMapLock;
 };
 
 } // namespace WebCore
 
 #endif // DatabaseManager_h