[net/base] Forward declaration of classes instead of including header

net/base/directory_lister.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_BASE_DIRECTORY_LISTER_H_
 #define NET_BASE_DIRECTORY_LISTER_H_
 
 #include <vector>
 
 #include "base/atomicops.h"
 #include "base/files/file_enumerator.h"
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
-#include "base/message_loop/message_loop_proxy.h"
 #include "net/base/net_export.h"
 
+namespace base {
+class MessageLoopProxy;
+}
+
 namespace net {
 
 // This class provides an API for asynchronously listing the contents of a
 // directory on the filesystem.  It runs a task on a background thread, and
 // enumerates all files in the specified directory on that thread.  Destroying
 // the lister cancels the list operation.  The DirectoryLister must only be
 // used on a thread with a MessageLoop.
 class NET_EXPORT DirectoryLister  {
  public:
   // Represents one file found.
@@ skipping 98 matching lines @@
 
   scoped_refptr<Core> core_;
   DirectoryListerDelegate* const delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(DirectoryLister);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_DIRECTORY_LISTER_H_