Presentation API: implement .getAvalability() (Blink side).

Source/modules/presentation/AvailableChangeEventInit.idl

Index: Source/modules/presentation/AvailableChangeEventInit.idl
diff --git a/Source/modules/presentation/AvailableChangeEventInit.idl b/Source/modules/presentation/AvailableChangeEventInit.idl
deleted file mode 100644
index 499c87e21588ced1a392b00082d9f28fc1f30611..0000000000000000000000000000000000000000
--- a/Source/modules/presentation/AvailableChangeEventInit.idl
+++ /dev/null
@@ -1,9 +0,0 @@
-// 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://w3c.github.io/presentation-api/#availablechangeevent
-
-dictionary AvailableChangeEventInit : EventInit {
-    boolean available = false;
-};