Add constructors for WebAudio nodes

third_party/WebKit/Source/modules/webaudio/ChannelMergerOptions.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.
 
-module ash.mojom;
-
-enum AshWindowType {
-  SHELF = 0,
-  STATUS_AREA,
-  COUNT
-};
-
-const string kAshWindowType_Property = "ash:window-type";
+// See https://webaudio.github.io/web-audio-api/#channelmergeroptions
+dictionary ChannelMergerOptions : AudioNodeOptions {
+    unsigned long numberOfInputs = 6;
+};