Makes SystemTray explicitly remove an AnimationObserver. Without this

ash/system/tray/system_tray.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/system/tray/system_tray.h"
 
 #include "ash/shell.h"
 #include "ash/shell/panel_window.h"
 #include "ash/shell_window_ids.h"
 #include "ash/system/audio/tray_volume.h"
@@ skipping 95 matching lines @@
       hide_notifications_(false) {
 }
 
 SystemTray::~SystemTray() {
   bubble_.reset();
   for (std::vector<SystemTrayItem*>::iterator it = items_.begin();
        it != items_.end();
        ++it) {
     (*it)->DestroyTrayView();
   }
+  GetWidget()->GetNativeView()->layer()->GetAnimator()->RemoveObserver(
+      layer_animation_observer_.get());
 }
 
 void SystemTray::Initialize() {
   layer_animation_observer_.reset(new SystemTrayLayerAnimationObserver(this));
   GetWidget()->GetNativeView()->layer()->GetAnimator()->AddObserver(
       layer_animation_observer_.get());
 }
 
 void SystemTray::CreateItems() {
   internal::TrayVolume* tray_volume = new internal::TrayVolume();
@@ skipping 377 matching lines @@
 
 void SystemTray::OnPaintFocusBorder(gfx::Canvas* canvas) {
   // The tray itself expands to the right and bottom edge of the screen to make
   // sure clicking on the edges brings up the popup. However, the focus border
   // should be only around the container.
   if (GetWidget() && GetWidget()->IsActive())
     DrawBorder(canvas, GetContentsBounds());
 }
 
 }  // namespace ash