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

ui/views/controls/button/blue_button.h

 // Copyright 2013 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_BUTTON_BLUE_BUTTON_H_
 #define UI_VIEWS_CONTROLS_BUTTON_BLUE_BUTTON_H_
 
 #include "base/compiler_specific.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "ui/views/controls/button/label_button.h"
 
 namespace views {
 
 // A class representing a blue button.
 class VIEWS_EXPORT BlueButton : public LabelButton {
  public:
   static const char kViewClassName[];
 
   BlueButton(ButtonListener* listener, const base::string16& text);
   virtual ~BlueButton();
 
  private:
   // Overridden from LabelButton:
   virtual const char* GetClassName() const OVERRIDE;
   virtual const ui::Animation* GetThemeAnimation() const OVERRIDE;
 
   DISALLOW_COPY_AND_ASSIGN(BlueButton);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_BUTTON_BLUE_BUTTON_H_