Add explicit destructor to DatabaseBackend.h.

Source/modules/webdatabase/DatabaseBackend.cpp

 /*
  * 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 29 matching lines @@
 
 namespace blink {
 
 DatabaseBackend::DatabaseBackend(DatabaseContext* databaseContext, const String& name, const String& expectedVersion, const String& displayName, unsigned long estimatedSize)
     : DatabaseBackendBase(databaseContext, name, expectedVersion, displayName, estimatedSize, DatabaseType::Async)
     , m_transactionInProgress(false)
     , m_isTransactionQueueEnabled(true)
 {
 }
 
+DatabaseBackend::~DatabaseBackend()
+{
+}
+
 void DatabaseBackend::trace(Visitor* visitor)
 {
     visitor->trace(m_transactionQueue);
     DatabaseBackendBase::trace(visitor);
 }
 
 bool DatabaseBackend::openAndVerifyVersion(bool setVersionInNewDatabase, DatabaseError& error, String& errorMessage)
 {
     TaskSynchronizer synchronizer;
     if (!databaseContext()->databaseThread() || databaseContext()->databaseThread()->terminationRequested(&synchronizer))
@@ skipping 102 matching lines @@
 {
     return databaseContext()->databaseThread()->transactionClient();
 }
 
 SQLTransactionCoordinator* DatabaseBackend::transactionCoordinator() const
 {
     return databaseContext()->databaseThread()->transactionCoordinator();
 }
 
 } // namespace blink