aura: Fix applist crash on 2nd show.

ash/app_list/app_list.cc

 // 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.
 
 #include "ash/app_list/app_list.h"
 
 #include "ash/app_list/app_list_model.h"
 #include "ash/app_list/app_list_view.h"
 #include "ash/ash_switches.h"
 #include "ash/shell_delegate.h"
@@ skipping 69 matching lines @@
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // AppList, private:
 
 void AppList::SetWidget(views::Widget* widget) {
   DCHECK(widget_ == NULL);
 
   if (is_visible_) {
     widget_ = widget;
-    GetLayer(widget_)->GetAnimator()->AddObserver(this);
+    widget_->AddObserver(this);
     Shell::GetInstance()->AddRootWindowEventFilter(this);
 
     widget_->SetBounds(GetPreferredBounds(false));
     widget_->SetOpacity(0);
     ScheduleAnimation();
 
     widget_->Show();
   } else {
     widget->Close();
   }
@@ skipping 81 matching lines @@
 }
 
 void AppList::OnWidgetActivationChanged(views::Widget* widget, bool active) {
   DCHECK(widget_ == widget);
   if (widget_ && is_visible_ && !active)
     SetVisible(false);
 }
 
 }  // namespace internal
 }  // namespace ash