Add NULL check in SystemTray::ShowDetailedView.

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/ash_switches.h"
 #include "ash/shell.h"
 #include "ash/shell/panel_window.h"
 #include "ash/shell_window_ids.h"
@@ skipping 220 matching lines @@
                             TrayBubbleView::InitParams::kArrowDefaultOffset);
 }
 
 void SystemTray::ShowDetailedView(SystemTrayItem* item,
                                   int close_delay,
                                   bool activate,
                                   BubbleCreationType creation_type) {
   std::vector<SystemTrayItem*> items;
   items.push_back(item);
   ShowItems(items, true, activate, creation_type, GetTrayXOffset(item));
-  system_bubble_->bubble()->StartAutoCloseTimer(close_delay);
+  if (system_bubble_.get())
+    system_bubble_->bubble()->StartAutoCloseTimer(close_delay);
 }
 
 void SystemTray::SetDetailedViewCloseDelay(int close_delay) {
   if (HasSystemBubbleType(SystemTrayBubble::BUBBLE_TYPE_DETAILED))
     system_bubble_->bubble()->StartAutoCloseTimer(close_delay);
 }
 
 void SystemTray::HideDetailedView(SystemTrayItem* item) {
   if (item != detailed_item_)
     return;
@@ skipping 330 matching lines @@
         ConvertPointToWidget(this, &point);
         arrow_offset = point.x();
       }
     }
     ShowDefaultViewWithOffset(BUBBLE_CREATE_NEW, arrow_offset);
   }
   return true;
 }
 
 }  // namespace ash