[Presentation API] make PresentationReceiver API consistent with latest spec

third_party/WebKit/Source/modules/presentation/PresentationConnectionList.idl

+// Copyright 2016 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.
+
+// This API was never implemented and has no known functional usages,
+// so this is a no-op as far as Web compatibility is concerned;
+// we should send an intent to ship when the implementation is further along.
+
+// https://w3c.github.io/presentation-api/#interface-presentationconnectionlist
+
+[
+    RuntimeEnabled=PresentationReceiver
+] interface PresentationConnectionList : EventTarget {
+    readonly attribute FrozenArray<PresentationConnection> connections;
+    attribute EventHandler onconnectionavailable;
+};