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

ui/views/widget/tooltip_manager_aura.h

 // Copyright (c) 2011 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_WIDGET_TOOLTIP_MANAGER_AURA_H_
 #define UI_VIEWS_WIDGET_TOOLTIP_MANAGER_AURA_H_
 
 #include "base/compiler_specific.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "ui/gfx/point.h"
 #include "ui/views/widget/tooltip_manager.h"
 
 namespace aura {
 class RootWindow;
 class Window;
 }
 
 namespace views {
 
@@ skipping 20 matching lines @@
   aura::Window* window_;
   Widget* widget_;
   string16 tooltip_text_;
 
   DISALLOW_COPY_AND_ASSIGN(TooltipManagerAura);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_TOOLTIP_MANAGER_AURA_H_