Use a direct include of strings headers in ui/, part 3.

ui/views/controls/tree/tree_view_unittest.cc

 // 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.
 
 #include "ui/views/controls/tree/tree_view.h"
 
 #include <string>
 
-#include "base/string_util.h"
+#include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "ui/base/models/tree_node_model.h"
 #include "ui/views/controls/textfield/textfield.h"
 #include "ui/views/controls/tree/tree_view_selector.h"
 #include "ui/views/test/views_test_base.h"
 
 using ui::TreeModel;
 using ui::TreeModelNode;
 using ui::TreeNode;
 
@@ skipping 391 matching lines @@
   tree_.SetSelectedNode(GetNodeByTitle("root"));
   ExpandOrSelectChild();
   tree_.SetEditable(true);
   tree_.StartEditing(GetNodeByTitle("a"));
   tree_.editor()->SetText(ASCIIToUTF16("a changed"));
   tree_.OnDidChangeFocus(NULL, NULL);
   EXPECT_TRUE(GetNodeByTitle("a changed") != NULL);
 }
 
 }  // namespace views