ash uber tray: Fix a couple of crashes when quitting.

chrome/browser/chromeos/system/ash_system_tray_delegate.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 "chrome/browser/chromeos/system/ash_system_tray_delegate.h"
 
 #include "ash/shell.h"
 #include "ash/system/audio/audio_controller.h"
 #include "ash/system/brightness/brightness_controller.h"
 #include "ash/system/tray/system_tray.h"
@@ skipping 14 matching lines @@
 class SystemTrayDelegate : public ash::SystemTrayDelegate,
                            public AudioHandler::VolumeObserver,
                            public PowerManagerClient::Observer {
  public:
   explicit SystemTrayDelegate(ash::SystemTray* tray) : tray_(tray) {
     AudioHandler::GetInstance()->AddVolumeObserver(this);
     DBusThreadManager::Get()->GetPowerManagerClient()->AddObserver(this);
   }
 
   virtual ~SystemTrayDelegate() {
-    AudioHandler::GetInstance()->RemoveVolumeObserver(this);
+    AudioHandler* audiohandler = AudioHandler::GetInstance();
+    if (audiohandler)
+      audiohandler->RemoveVolumeObserver(this);
     DBusThreadManager::Get()->GetPowerManagerClient()->RemoveObserver(this);
   }
 
   // Overridden from ash::SystemTrayDelegate.
   virtual const std::string GetUserDisplayName() OVERRIDE {
     return UserManager::Get()->logged_in_user().GetDisplayName();
   }
 
   virtual const std::string GetUserEmail() OVERRIDE {
     return UserManager::Get()->logged_in_user().email();
@@ skipping 62 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(SystemTrayDelegate);
 };
 
 }  // namespace
 
 ash::SystemTrayDelegate* CreateSystemTrayDelegate(ash::SystemTray* tray) {
   return new chromeos::SystemTrayDelegate(tray);
 }
 
 }  // namespace chromeos