Make the Get Alarm Callback Parameter Optional

chrome/common/extensions/api/alarms.idl

 // 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.
 
 // Use the <code>chrome.alarms</code> API to schedule code to run
 // periodically or at a specified time in the future.
 namespace alarms {
   dictionary Alarm {
     // Name of this alarm.
     DOMString name;
@@ skipping 22 matching lines @@
     double? delayInMinutes;
 
     // If set, the onAlarm event should fire every <var>periodInMinutes</var>
     // minutes after the initial event specified by <var>when</var> or
     // <var>delayInMinutes</var>.  If not set, the alarm will only fire once.
     //
     // <!-- TODO: need minimum=0 -->
     double? periodInMinutes;
   };
 
-  callback AlarmCallback = void (Alarm alarm);
+  callback AlarmCallback = void (optional Alarm alarm);
   callback AlarmListCallback = void (Alarm[] alarms);
   callback ClearCallback = void (boolean wasCleared);
 
   interface Functions {
     // Creates an alarm.  Near the time(s) specified by <var>alarmInfo</var>,
     // the <code>onAlarm</code> event is fired. If there is another alarm with
     // the same name (or no name if none is specified), it will be cancelled and
     // replaced by this alarm.
     //
     // In order to reduce the load on the user's machine, Chrome limits alarms
@@ skipping 33 matching lines @@
     // Clears all alarms.
     static void clearAll(optional ClearCallback callback);
   };
 
   interface Events {
     // Fired when an alarm has elapsed. Useful for event pages.
     // |alarm|: The alarm that has elapsed.
     static void onAlarm(Alarm alarm);
   };
 };