Implement onunhandledrejection / onrejectionhandled events

Source/core/events/PromiseRejectionEvent.idl

Index: Source/core/events/PromiseRejectionEvent.idl
diff --git a/Source/core/events/PromiseRejectionEvent.idl b/Source/core/events/PromiseRejectionEvent.idl
new file mode 100644
index 0000000000000000000000000000000000000000..641fc73999b376aad4d94627ed250f0d634444bf
--- /dev/null
+++ b/Source/core/events/PromiseRejectionEvent.idl
@@ -0,0 +1,14 @@
+// Copyright 2015 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.
+
+// https://github.com/domenic/unhandled-rejections-browser-spec
+
+[
+    RuntimeEnabled=PromiseRejectionEvent,
+    Constructor(DOMString type, optional PromiseRejectionEventInit eventInitDict),
+    Exposed=(Window,Worker,ServiceWorker),
+] interface PromiseRejectionEvent : Event {
+    readonly attribute Promise<any> promise;
+    readonly attribute any reason;
+};