Revert of Remove the concept of a cleanup task

Source/modules/webdatabase/DatabaseThread.cpp

Index: Source/modules/webdatabase/DatabaseThread.cpp
diff --git a/Source/modules/webdatabase/DatabaseThread.cpp b/Source/modules/webdatabase/DatabaseThread.cpp
index 810e198fb0eec9b31549b06d78d14b7e1554dac1..f6dc627c9aab273791dc6831e4379b7ee4b3c7d3 100644
--- a/Source/modules/webdatabase/DatabaseThread.cpp
+++ b/Source/modules/webdatabase/DatabaseThread.cpp
@@ -71,7 +71,7 @@
 
 void DatabaseThread::setupDatabaseThread()
 {
-    m_thread->initialize();
+    m_thread->attachGC();
 }
 
 void DatabaseThread::terminate()
@@ -122,7 +122,7 @@
 
 void DatabaseThread::cleanupDatabaseThreadCompleted()
 {
-    m_thread->shutdown();
+    m_thread->detachGC();
     if (m_cleanupSync) // Someone wanted to know when we were done cleaning up.
         m_cleanupSync->taskCompleted();
 }