Add constructors for WebAudio nodes

third_party/WebKit/Source/modules/webaudio/IIRFilterNode.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.
 
+// See https://webaudio.github.io/web-audio-api/#the-iirfilternode-interface
+[
+    Constructor(BaseAudioContext context, IIRFilterOptions options),
+    RaisesException=Constructor,
+]
 interface IIRFilterNode : AudioNode {
     [RaisesException] void getFrequencyResponse(Float32Array frequencyHz,
                                                 Float32Array magResponse,
                                                 Float32Array phaseResponse);
 };