Make DatabaseTask inherit from WebTask

Source/modules/webdatabase/DatabaseThread.cpp

 /*
  * Copyright (C) 2007, 2008, 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
@@ skipping 89 matching lines @@
 void DatabaseThread::databaseThread()
 {
     {
         // Wait for DatabaseThread::start() to complete.
         MutexLocker lock(m_threadCreationMutex);
         LOG(StorageAPI, "Started DatabaseThread %p", this);
     }
 
     AutodrainedPool pool;
     while (OwnPtr<DatabaseTask> task = m_queue.waitForMessage()) {
-        task->performTask();
+        task->run();
         pool.cycle();
     }
 
     // Clean up the list of all pending transactions on this database thread
     m_transactionCoordinator->shutdown();
 
     LOG(StorageAPI, "About to detach thread %i and clear the ref to DatabaseThread %p, which currently has %i ref(s)", m_threadID, this, refCount());
 
     // Close the databases that we ran transactions on. This ensures that if any transactions are still open, they are rolled back and we don't leave the database in an
     // inconsistent or locked state.
@@ skipping 55 matching lines @@
 };
 
 void DatabaseThread::unscheduleDatabaseTasks(DatabaseBackend* database)
 {
     // Note that the thread loop is running, so some tasks for the database
     // may still be executed. This is unavoidable.
     SameDatabasePredicate predicate(database);
     m_queue.removeIf(predicate);
 }
 } // namespace WebCore