Implement EventSource and update test expectations

components/script/dom/webidls/EventSource.webidl

@@ -0,0 +1,31 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+/*
+ * The origin of this IDL file is:
+ * https://html.spec.whatwg.org/multipage/#eventsource
+ */
+
+[Constructor(DOMString url, optional EventSourceInit eventSourceInitDict),
+/*Exposed=(Window,Worker)*/]
+interface EventSource : EventTarget {
+  readonly attribute DOMString url;
+  readonly attribute boolean withCredentials;
+
+  // ready state
+  const unsigned short CONNECTING = 0;
+  const unsigned short OPEN = 1;
+  const unsigned short CLOSED = 2;
+  readonly attribute unsigned short readyState;
+
+  // networking
+  attribute EventHandler onopen;
+  attribute EventHandler onmessage;
+  attribute EventHandler onerror;
+  void close();
+};
+
+dictionary EventSourceInit {
+  boolean withCredentials = false;
+};