Use a direct include of strings headers in ui/, part 2.

ui/base/models/tree_node_model.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 UI_BASE_MODELS_TREE_NODE_MODEL_H_
 #define UI_BASE_MODELS_TREE_NODE_MODEL_H_
 
 #include <algorithm>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/scoped_vector.h"
 #include "base/observer_list.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "ui/base/models/tree_model.h"
 
 namespace ui {
 
 // TreeNodeModel and TreeNodes provide an implementation of TreeModel around
 // TreeNodes.
 //
 // TreeNodes own their children, so that deleting a node deletes all
 // descendants.
 //
@@ skipping 267 matching lines @@
 
   // The root.
   scoped_ptr<NodeType> root_;
 
   DISALLOW_COPY_AND_ASSIGN(TreeNodeModel);
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_MODELS_TREE_NODE_MODEL_H_