Modify UpdateLibrary to use async RequestUpdateCheck call

chrome/browser/chromeos/login/update_screen.h

 // Copyright (c) 2010 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.
 
 #ifndef CHROME_BROWSER_CHROMEOS_LOGIN_UPDATE_SCREEN_H_
 #define CHROME_BROWSER_CHROMEOS_LOGIN_UPDATE_SCREEN_H_
 #pragma once
 
 #include "base/timer.h"
 #include "chrome/browser/chromeos/cros/update_library.h"
@@ skipping 42 matching lines @@
   void SetRebootCheckDelay(int seconds);
 
   // Returns true if there is critical system update that requires installation
   // and immediate reboot.
   bool HasCriticalUpdate();
 
   // Set flag to treat all updates as critical (for test purpose mainly).
   // Default value is false.
   void SetAllUpdatesCritical(bool is_critical);
 
+  // Returns true if this instance is still active (i.e. has not been deleted).
+  static bool HasInstance(UpdateScreen* inst);
+
  private:
   // Timer notification handlers.
   void OnWaitForRebootTimeElapsed();
 
   // Checks that screen is shown, shows if not.
   void MakeSureScreenIsShown();
 
   // Timer for the interval to wait for the reboot.
   // If reboot didn't happen - ask user to reboot manually.
   base::OneShotTimer<UpdateScreen> reboot_timer_;
 
+  // Returns a static InstanceSet.
+  typedef std::set<UpdateScreen*> InstanceSet;
+  static InstanceSet& GetInstanceSet();
+
   // True if in the process of checking for update.
   bool checking_for_update_;
 
   // Time in seconds after which we decide that the device has not rebooted
   // automatically. If reboot didn't happen during this interval, ask user to
   // reboot device manually.
   int reboot_check_delay_;
 
   // Flag that is used to detect when update download has just started.
   bool is_downloading_update_;
 
   // Is all updates critical? If true, update deadlines are ignored.
   bool is_all_updates_critical_;
 
   DISALLOW_COPY_AND_ASSIGN(UpdateScreen);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_UPDATE_SCREEN_H_