Splitting out the Audio library.

tests/html/audiocontext_test.dart

 library AudioContextTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
+import 'dart:web_audio';
 
 main() {
 
   useHtmlConfiguration();
 
   var isAudioContext =
       predicate((x) => x is AudioContext, 'is an AudioContext');
 
   test('constructorTest', () {
       var ctx = new AudioContext();
@@ skipping 19 matching lines @@
     expect(gainNode is GainNode, isTrue);
 
     expect(context.createAnalyser() is AnalyserNode, isTrue);
     expect(context.createChannelMerger() is ChannelMergerNode, isTrue);
     expect(context.createChannelSplitter() is ChannelSplitterNode, isTrue);
     expect(context.createOscillator() is OscillatorNode, isTrue);
     expect(context.createPanner() is PannerNode, isTrue);
     expect(context.createScriptProcessor(4096) is ScriptProcessorNode, isTrue);
   });
 }