Replace more ObserverList with base::ObserverList.

ui/views/widget/desktop_aura/desktop_window_tree_host_x11.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_WIDGET_DESKTOP_AURA_DESKTOP_WINDOW_TREE_HOST_X11_H_
 #define UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_WINDOW_TREE_HOST_X11_H_
 
 #include <X11/extensions/shape.h>
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>
@@ skipping 301 matching lines @@
 
   DesktopNativeWidgetAura* desktop_native_widget_aura_;
 
   aura::Window* content_window_;
 
   // We can optionally have a parent which can order us to close, or own
   // children who we're responsible for closing when we CloseNow().
   DesktopWindowTreeHostX11* window_parent_;
   std::set<DesktopWindowTreeHostX11*> window_children_;
 
-  ObserverList<DesktopWindowTreeHostObserverX11> observer_list_;
+  base::ObserverList<DesktopWindowTreeHostObserverX11> observer_list_;
 
   // The window shape if the window is non-rectangular.
   gfx::XScopedPtr<_XRegion, gfx::XObjectDeleter<_XRegion, int, XDestroyRegion>>
       window_shape_;
 
   // Whether |window_shape_| was set via SetShape().
   bool custom_window_shape_;
 
   // The size of the window manager provided borders (if any).
   gfx::Insets native_window_frame_borders_in_pixels_;
@@ skipping 17 matching lines @@
   base::CancelableCallback<void()> delayed_resize_task_;
 
   base::WeakPtrFactory<DesktopWindowTreeHostX11> close_widget_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DesktopWindowTreeHostX11);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_WINDOW_TREE_HOST_X11_H_