Prefix string16 with base:: in ui/.

ui/views/views_delegate.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_VIEWS_DELEGATE_H_
 #define UI_VIEWS_VIEWS_DELEGATE_H_
 
 #include <string>
 
 #if defined(OS_WIN)
@@ skipping 62 matching lines @@
       const std::string& window_name,
       gfx::Rect* bounds,
       ui::WindowShowState* show_state) const = 0;
 
   virtual void NotifyAccessibilityEvent(
       View* view,
       ui::AccessibilityTypes::Event event_type) = 0;
 
   // For accessibility, notify the delegate that a menu item was focused
   // so that alternate feedback (speech / magnified text) can be provided.
-  virtual void NotifyMenuItemFocused(const string16& menu_name,
-                                     const string16& menu_item_name,
+  virtual void NotifyMenuItemFocused(const base::string16& menu_name,
+                                     const base::string16& menu_item_name,
                                      int item_index,
                                      int item_count,
                                      bool has_submenu) = 0;
 
 #if defined(OS_WIN)
   // Retrieves the default window icon to use for windows if none is specified.
   virtual HICON GetDefaultWindowIcon() const = 0;
   // Returns true if the window passed in is in the Windows 8 metro
   // environment.
   virtual bool IsWindowInMetro(gfx::NativeWindow window) const = 0;
@@ skipping 24 matching lines @@
   // Returns the default obscured text reveal duration.
   virtual base::TimeDelta GetDefaultTextfieldObscuredRevealDuration() = 0;
 
  private:
   scoped_ptr<ViewsTouchSelectionControllerFactory> views_tsc_factory_;
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_VIEWS_DELEGATE_H_