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

ui/views/controls/textfield/textfield_views_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_VIEWS_CONTROLS_TEXTFIELD_TEXTFIELD_VIEWS_MODEL_H_
 #define UI_VIEWS_CONTROLS_TEXTFIELD_TEXTFIELD_VIEWS_MODEL_H_
 
 #include <list>
 #include <vector>
 
 #include "base/gtest_prod_util.h"
 #include "base/memory/scoped_ptr.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/base/ime/composition_text.h"
 #include "ui/gfx/rect.h"
 #include "ui/gfx/render_text.h"
 #include "ui/gfx/text_constants.h"
 #include "ui/views/views_export.h"
 
 namespace gfx {
 class RenderText;
 }  // namespace gfx
@@ skipping 283 matching lines @@
   // 2) new edit is added. (redo history is cleared)
   // 3) redone all undone edits.
   EditHistory::iterator current_edit_;
 
   DISALLOW_COPY_AND_ASSIGN(TextfieldViewsModel);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_TEXTFIELD_TEXTFIELD_VIEWS_MODEL_H_