Replace more ObserverList with base::ObserverList.

ui/aura/window_tree_host.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_AURA_WINDOW_TREE_HOST_H_
 #define UI_AURA_WINDOW_TREE_HOST_H_
 
 #include <vector>
 
 #include "base/event_types.h"
@@ skipping 162 matching lines @@
   // by MoveCursorTo() and MoveCursorToHostLocation().
   void MoveCursorToInternal(const gfx::Point& root_location,
                             const gfx::Point& host_location);
 
   // We don't use a scoped_ptr for |window_| since we need this ptr to be valid
   // during its deletion. (Window's dtor notifies observers that may attempt to
   // reach back up to access this object which will be valid until the end of
   // the dtor).
   Window* window_;  // Owning.
 
-  ObserverList<WindowTreeHostObserver> observers_;
+  base::ObserverList<WindowTreeHostObserver> observers_;
 
   scoped_ptr<WindowEventDispatcher> dispatcher_;
 
   scoped_ptr<ui::Compositor> compositor_;
 
   // Last cursor set.  Used for testing.
   gfx::NativeCursor last_cursor_;
   gfx::Point last_cursor_request_position_in_host_;
 
   scoped_ptr<ui::ViewProp> prop_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowTreeHost);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_WINDOW_TREE_HOST_H_