Convert decodeAudioData to return a Future.

sdk/lib/web_audio/dart2js/web_audio_dart2js.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:typed_data';
 import 'dart:_js_helper' show Creates, JSName, Returns, convertDartClosureToJS;
 import 'dart:_foreign_helper' show JS;
@@ skipping 308 matching lines @@
   PannerNode createPanner() native;
 
   @DomName('AudioContext.createWaveShaper')
   @DocsEditable()
   WaveShaperNode createWaveShaper() native;
 
   @DomName('AudioContext.createWaveTable')
   @DocsEditable()
   WaveTable createWaveTable(Float32List real, Float32List imag) native;
 
+  @JSName('decodeAudioData')
   @DomName('AudioContext.decodeAudioData')
   @DocsEditable()
-  void decodeAudioData(ByteBuffer audioData, AudioBufferCallback successCallback, [AudioBufferCallback errorCallback]) native;
+  void _decodeAudioData(ByteBuffer audioData, AudioBufferCallback successCallback, [AudioBufferCallback errorCallback]) native;
+
+  @JSName('decodeAudioData')
+  @DomName('AudioContext.decodeAudioData')
+  @DocsEditable()
+  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;
 
   @DomName('AudioContext.oncomplete')
   @DocsEditable()
   Stream<Event> get onComplete => completeEvent.forTarget(this);
 
   factory AudioContext() => JS('AudioContext',
@@ skipping 773 matching lines @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 
 @DocsEditable()
 @DomName('WaveTable')
 // https://dvcs.w3.org/hg/audio/raw-file/tip/webaudio/specification.html#WaveTable-section
 @Experimental()
 class WaveTable extends Interceptor native "WaveTable" {
 }