Update supported browser annotations for Firefox Web Audio.

sdk/lib/web_audio/dart2js/web_audio_dart2js.dart

 /**
  * High-fidelity audio programming in the browser.
  */
 library dart.dom.web_audio;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:_internal' hide deprecated;
 import 'dart:html';
 import 'dart:html_common';
@@ skipping 97 matching lines @@
 @DomName('AudioBufferCallback')
 // https://dvcs.w3.org/hg/audio/raw-file/tip/webaudio/specification.html#AudioBuffer-section
 @Experimental()
 typedef void AudioBufferCallback(AudioBuffer audioBuffer);
 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // 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.
 
 
 @DomName('AudioBufferSourceNode')
+@SupportedBrowser(SupportedBrowser.CHROME)
+@SupportedBrowser(SupportedBrowser.FIREFOX)
+@Experimental()
 // https://dvcs.w3.org/hg/audio/raw-file/tip/webaudio/specification.html#AudioBufferSourceNode-section
-@Experimental()
 class AudioBufferSourceNode extends AudioSourceNode native "AudioBufferSourceNode" {
 
   // TODO(efortuna): Remove these methods when Chrome stable also uses start
   // instead of noteOn.
   void start(num when, [num grainOffset, num grainDuration]) {
     if (JS('bool', '!!#.start', this)) {
       if (grainDuration != null) {
         JS('void', '#.start(#, #, #)', this, when, grainOffset, grainDuration);
       } else if (grainOffset != null) {
         JS('void', '#.start(#, #)', this, when, grainOffset);
@@ skipping 86 matching lines @@
   @Experimental() // untriaged
   Stream<Event> get onEnded => endedEvent.forTarget(this);
 
 }
 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // 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.
 
 
 @DomName('AudioContext')
+@SupportedBrowser(SupportedBrowser.CHROME)
+@SupportedBrowser(SupportedBrowser.FIREFOX)
+@Experimental()
 // https://dvcs.w3.org/hg/audio/raw-file/tip/webaudio/specification.html#AudioContext-section
-@Experimental()
 class AudioContext extends EventTarget native "AudioContext,webkitAudioContext" {
   // To suppress missing implicit constructor warnings.
   factory AudioContext._() { throw new UnsupportedError("Not supported"); }
 
   /**
    * Static factory designed to expose `complete` events to event
    * handlers that are not necessarily instances of [AudioContext].
    *
    * See [EventStreamProvider] for usage information.
    */
@@ skipping 817 matching lines @@
   factory WaveShaperNode._() { throw new UnsupportedError("Not supported"); }
 
   @DomName('WaveShaperNode.curve')
   @DocsEditable()
   Float32List curve;
 
   @DomName('WaveShaperNode.oversample')
   @DocsEditable()
   String oversample;
 }