Add explicit destructor to DatabaseBackend.h.

Source/modules/webdatabase/DatabaseBackend.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 31 matching lines @@
 
 // FIXME: This implementation of DatabaseBackend is only a place holder
 // for the split out of the Database backend to be done later. This
 // place holder is needed to allow other code that need to reference the
 // DatabaseBackend to do so before the proper backend split is
 // available. This should be replaced with the actual implementation later.
 
 class DatabaseBackend : public DatabaseBackendBase {
 public:
     DatabaseBackend(DatabaseContext*, const String& name, const String& expectedVersion, const String& displayName, unsigned long estimatedSize);
+    virtual ~DatabaseBackend();
     virtual void trace(Visitor*) OVERRIDE;
 
     virtual bool openAndVerifyVersion(bool setVersionInNewDatabase, DatabaseError&, String& errorMessage) OVERRIDE FINAL;
     void close();
 
     PassRefPtrWillBeRawPtr<SQLTransactionBackend> runTransaction(PassRefPtrWillBeRawPtr<SQLTransaction>, bool readOnly, const ChangeVersionData*);
     void scheduleTransactionStep(SQLTransactionBackend*);
     void inProgressTransactionCompleted();
 
     SQLTransactionClient* transactionClient() const;
@@ skipping 13 matching lines @@
     Mutex m_transactionInProgressMutex;
     bool m_transactionInProgress;
     bool m_isTransactionQueueEnabled;
 
     friend class Database;
 };
 
 } // namespace blink
 
 #endif // DatabaseBackend_h