Bug 1100895 - Part 1: Replace 'ready' event by a readonly attribute 'ready'. r=hsinyi

dom/webidl/Telephony.webidl

@@ -46,8 +46,9 @@ interface Telephony : EventTarget {
   readonly attribute CallsList calls;
   readonly attribute TelephonyCallGroup conferenceGroup;
 
-  // The 'ready' event will be fired when the telephony object is ready.
-  attribute EventHandler onready;
+  // Async notification that object initialization is done.
+  [Throws]
+  readonly attribute Promise<void> ready;
 
   attribute EventHandler onincoming;
   attribute EventHandler oncallschanged;