Convert decodeAudioData to return a Future.

sdk/lib/web_audio/dartium/web_audio_dartium.dart

 library dart.dom.web_audio;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:_collection-dev' hide deprecated;
 import 'dart:html';
 import 'dart:html_common';
 import 'dart:nativewrappers';
 import 'dart:typed_data';
 // DO NOT EDIT
@@ skipping 414 matching lines @@
   @DomName('AudioContext.createWaveShaper')
   @DocsEditable()
   WaveShaperNode createWaveShaper() native "AudioContext_createWaveShaper_Callback";
 
   @DomName('AudioContext.createWaveTable')
   @DocsEditable()
   WaveTable createWaveTable(Float32List real, Float32List imag) native "AudioContext_createWaveTable_Callback";
 
   @DomName('AudioContext.decodeAudioData')
   @DocsEditable()
-  void decodeAudioData(ByteBuffer audioData, AudioBufferCallback successCallback, [AudioBufferCallback errorCallback]) native "AudioContext_decodeAudioData_Callback";
+  void _decodeAudioData(ByteBuffer audioData, AudioBufferCallback successCallback, [AudioBufferCallback errorCallback]) native "AudioContext_decodeAudioData_Callback";
+
+  Future<AudioBuffer> decodeAudioData(ByteBuffer audioData) {
+    var completer = new Completer<AudioBuffer>();
+    _decodeAudioData(audioData,
+        (value) { completer.complete(value); },
+        (error) { completer.completeError(error); });
+    return completer.future;
+  }
 
   @DomName('AudioContext.startRendering')
   @DocsEditable()
   void startRendering() native "AudioContext_startRendering_Callback";
 
   @DomName('AudioContext.oncomplete')
   @DocsEditable()
   Stream<Event> get onComplete => completeEvent.forTarget(this);
 
 }
@@ skipping 902 matching lines @@
 // WARNING: Do not edit - generated code.
 
 
 @DocsEditable()
 @DomName('WaveTable')
 // https://dvcs.w3.org/hg/audio/raw-file/tip/webaudio/specification.html#WaveTable-section
 @Experimental()
 class WaveTable extends NativeFieldWrapperClass1 {
 
 }