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

ui/views/controls/textfield/textfield.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_H_
 #define UI_VIEWS_CONTROLS_TEXTFIELD_TEXTFIELD_H_
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "base/time.h"
 #include "build/build_config.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/base/ime/text_input_type.h"
 #include "ui/base/keycodes/keyboard_codes.h"
 #include "ui/gfx/font.h"
 #include "ui/gfx/native_widget_types.h"
 #include "ui/gfx/text_constants.h"
 #include "ui/views/controls/textfield/native_textfield_wrapper.h"
 #include "ui/views/view.h"
@@ skipping 342 matching lines @@
 
   // The duration to reveal the last typed char for obscured textfields.
   base::TimeDelta obscured_reveal_duration_;
 
   DISALLOW_COPY_AND_ASSIGN(Textfield);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_TEXTFIELD_TEXTFIELD_H_