Define default values for options dictionaries for WebAudio

third_party/WebKit/Source/modules/webaudio/DynamicsCompressorOptions.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/#dynamicscompressoroptions
 dictionary DynamicsCompressorOptions : AudioNodeOptions {
-    float attack;
-    float knee;
-    float ratio;
-    float release;
-    float threshold;
+    float attack = 0.003;
+    float knee = 30;
+    float ratio = 12;
+    float release = 0.25;
+    float threshold = -24;
 };