Define default values for options dictionaries for WebAudio

third_party/WebKit/Source/modules/webaudio/PannerOptions.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/#panneroptions
 dictionary PannerOptions : AudioNodeOptions {
-    PanningModelType panningModel;
-    DistanceModelType distanceModel;
+    PanningModelType panningModel = "equalpower";
+    DistanceModelType distanceModel = "inverse";
 
-    float positionX;
-    float positionY;
-    float positionZ;
-    float orientationX;
-    float orientationY;
-    float orientationZ;
+    float positionX = 0;
+    float positionY = 0;
+    float positionZ = 0;
+    float orientationX = 1;
+    float orientationY = 0;
+    float orientationZ = 0;
 
-    double refDistance;
-    double maxDistance;
-    double rolloffFactor;
-    double coneInnerAngle;
-    double coneOuterAngle;
-    double coneOuterGain;
+    double refDistance = 1;
+    double maxDistance= 10000;
+    double rolloffFactor = 1;
+    double coneInnerAngle = 360;
+    double coneOuterAngle = 360;
+    double coneOuterGain = 0;
 };