Oilpan: DatabaseThread::m_thread should not get destructed during sweeping

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 92bd6faaafd082a2364a2d812cd30e194366c29b..c30b10b7d670fbd081cd98464885b06a77d6f5c3 100644
--- a/Source/modules/webdatabase/DatabaseThread.cpp
+++ b/Source/modules/webdatabase/DatabaseThread.cpp
@@ -51,13 +51,7 @@ DatabaseThread::DatabaseThread()
 DatabaseThread::~DatabaseThread()
 {
     ASSERT(m_openDatabaseSet.isEmpty());
-    // Oilpan: The database thread must have finished its cleanup tasks before
-    // the following clear(). Otherwise, WebThread destructor blocks the caller
-    // thread, and causes a deadlock with ThreadState cleanup.
-    // DatabaseContext::stop() asks the database thread to close all of
-    // databases, and wait until GC heap cleanup of the database thread. So we
-    // can safely destruct WebThread here.
-    m_thread.clear();
+    ASSERT(!m_thread);
 }
 
 void DatabaseThread::trace(Visitor* visitor)
@@ -68,6 +62,14 @@ void DatabaseThread::trace(Visitor* visitor)
 #endif
 }
 
+void DatabaseThread::dispose()
+{
+    // Oilpan: The database thread must have finished its cleanup tasks before
+    // the following clear(). Otherwise, the WebThread destructor blocks the
+    // caller thread, and causes a deadlock with ThreadState cleanup.
+    m_thread.clear();
+}
+
 void DatabaseThread::start()
 {
     if (m_thread)