Replace more ObserverList with base::ObserverList.

ash/first_run/first_run_helper.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 ASH_FIRST_RUN_FIRST_RUN_HELPER_H_
 #define ASH_FIRST_RUN_FIRST_RUN_HELPER_H_
 
 #include "ash/ash_export.h"
 #include "base/basictypes.h"
 #include "base/observer_list.h"
@@ skipping 53 matching lines @@
 
   // Returns bounds of system tray bubble. You must open bubble before calling
   // this method.
   virtual gfx::Rect GetTrayBubbleBounds() = 0;
 
   // Returns bounds of help app button from system tray buble. You must open
   // bubble before calling this method.
   virtual gfx::Rect GetHelpButtonBounds() = 0;
 
  protected:
-  ObserverList<Observer>& observers() { return observers_; }
+  base::ObserverList<Observer>& observers() { return observers_; }
 
  private:
-  ObserverList<Observer> observers_;
+  base::ObserverList<Observer> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(FirstRunHelper);
 };
 
 }  // namespace ash
 
 #endif  // ASH_FIRST_RUN_FIRST_RUN_HELPER_H_