Clean up forward declarations in Source/modules

Source/modules/webdatabase/DatabaseThread.h

Index: Source/modules/webdatabase/DatabaseThread.h
diff --git a/Source/modules/webdatabase/DatabaseThread.h b/Source/modules/webdatabase/DatabaseThread.h
index 3aed29381da1d4cfd1e07e2652e375875db0969b..f362d253b1e2a3ce16eb8ab535db103eea299757 100644
--- a/Source/modules/webdatabase/DatabaseThread.h
+++ b/Source/modules/webdatabase/DatabaseThread.h
@@ -29,21 +29,13 @@
 #define DatabaseThread_h
 
 #include "platform/WebThreadSupportingGC.h"
-#include "platform/heap/Handle.h"
-#include "wtf/Deque.h"
-#include "wtf/HashMap.h"
-#include "wtf/HashSet.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/PassOwnPtr.h"
-#include "wtf/ThreadingPrimitives.h"
 
 namespace blink {
 
 class Database;
 class DatabaseTask;
-class Document;
-class MessageLoopInterruptor;
-class PendingGCRunner;
 class SQLTransactionClient;
 class SQLTransactionCoordinator;
 class TaskSynchronizer;