Add check to identify the cause of the crash.

ash/common/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/common/system/tray/system_tray.h"
 
 #include "ash/common/key_event_watcher.h"
 #include "ash/common/login_status.h"
 #include "ash/common/material_design/material_design_controller.h"
 #include "ash/common/session/session_state_delegate.h"
@@ skipping 400 matching lines @@
 bool SystemTray::IsMouseInNotificationBubble() const {
   if (!notification_bubble_)
     return false;
   return notification_bubble_->bubble_view()->GetBoundsInScreen().Contains(
       display::Screen::GetScreen()->GetCursorScreenPoint());
 }
 
 bool SystemTray::CloseSystemBubble() const {
   if (!system_bubble_)
     return false;
+  CHECK(!activating_);
   system_bubble_->bubble()->Close();
   return true;
 }
 
 views::View* SystemTray::GetHelpButtonView() const {
   return tray_date_->GetHelpButtonView();
 }
 
 TrayAudio* SystemTray::GetTrayAudio() const {
   return tray_audio_;
@@ skipping 354 matching lines @@
   return tray_update_;
 }
 
 void SystemTray::CloseBubble(const ui::KeyEvent& key_event) {
   CloseSystemBubble();
 }
 
 void SystemTray::ActivateAndStartNavigation(const ui::KeyEvent& key_event) {
   if (!system_bubble_)
     return;
+  activating_ = true;
   ActivateBubble();
+  activating_ = false;
+  // TODO(oshima): This is to troubleshoot the issue crbug.com/651242. Remove
+  // once the root cause is fixed.
+  CHECK(system_bubble_) << " the bubble was deleted while activaing it";
+
   views::Widget* widget = GetSystemBubble()->bubble_view()->GetWidget();
   widget->GetFocusManager()->OnKeyEvent(key_event);
 }
 
 void SystemTray::CreateKeyEventWatcher() {
   key_event_watcher_ = WmShell::Get()->CreateKeyEventWatcher();
   // mustash does not yet support KeyEventWatcher. http://crbug.com/649600.
   if (!key_event_watcher_)
     return;
   key_event_watcher_->AddKeyEventCallback(
@@ skipping 32 matching lines @@
       }
     }
     ShowDefaultViewWithOffset(BUBBLE_CREATE_NEW, arrow_offset, false);
     if (event.IsKeyEvent())
       ActivateBubble();
   }
   return true;
 }
 
 void SystemTray::CloseSystemBubbleAndDeactivateSystemTray() {
+  CHECK(!activating_);
   activation_observer_.reset();
   key_event_watcher_.reset();
   system_bubble_.reset();
   // When closing a system bubble with the alternate shelf layout, we need to
   // turn off the active tinting of the shelf.
   if (full_system_tray_menu_) {
     SetDrawBackgroundAsActive(false);
     full_system_tray_menu_ = false;
   }
 }
@@ skipping 19 matching lines @@
           .work_area()
           .height();
   if (work_area_height > 0) {
     UMA_HISTOGRAM_CUSTOM_COUNTS(
         "Ash.SystemMenu.PercentageOfWorkAreaHeightCoveredByMenu",
         100 * bubble_view->height() / work_area_height, 1, 300, 100);
   }
 }
 
 }  // namespace ash