Implement onunhandledrejection / onrejectionhandled events

Source/core/frame/WindowEventHandlers.idl

 /*
  * Copyright (c) 2013, Opera Software ASA. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 28 matching lines @@
     // FIXME: onbeforeunload should be an OnBeforeUnloadEventHandler.
     attribute EventHandler onbeforeunload;
     attribute EventHandler onhashchange;
     attribute EventHandler onlanguagechange;
     attribute EventHandler onmessage;
     attribute EventHandler onoffline;
     attribute EventHandler ononline;
     attribute EventHandler onpagehide;
     attribute EventHandler onpageshow;
     attribute EventHandler onpopstate;
+    [RuntimeEnabled=PromiseRejectionEvent] attribute EventHandler onrejectionhandled;

[philipj_slow, 2015/06/16 14:58:03]

Here and in WorkerGlobalScope.idl, can you put the added things in a section at
the bottom called "Unhandled Rejection Tracking" or similar that links to
https://github.com/domenic/unhandled-rejections-browser-spec? (To make it easier
to track which bits come from which spec.)

[jochen (gone - plz use gerrit), 2015/06/17 07:57:53]

done

     attribute EventHandler onstorage;
+    [RuntimeEnabled=PromiseRejectionEvent] attribute EventHandler onunhandledrejection;
     attribute EventHandler onunload;
 };