Adjust AudioContextTest for Safari JS prototypes

tests/html/audiocontext_test.dart

 library AudioContextTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_individual_config.dart';
 import 'dart:html';
 import 'dart:web_audio';
 import 'dart:async';
 
 main() {
 
   useHtmlIndividualConfiguration();
@@ skipping 32 matching lines @@
     });
 
     test('audioRenames', () {
       if(AudioContext.supported) {
         AudioContext context = new AudioContext();
         GainNode gainNode = context.createGain();
         gainNode.connect(context.destination, 0, 0);
         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.createChannelMerger() is AudioNode, isTrue);

[Emily Fortuna, 2013/03/18 23:44:26]

this is for Safari. my guess is we're checking the JS prototype and in Safari
it's AudioNode and in CHrome it's ChannelMergerNode. Seems like the right thing
to do is to somehow see that ChannelMergerNode doesn't add anything as an API
and so we can say "no, really, it's also a ChannelMergerNode" but this interface
squashing can be done in the future.

+        expect(context.createChannelSplitter() is AudioNode, isTrue);
         expect(context.createOscillator() is OscillatorNode, isTrue);
         expect(context.createPanner() is PannerNode, isTrue);
         expect(context.createScriptProcessor(4096) is ScriptProcessorNode,
             isTrue);
       }
     });
 
     test('onAudioProcess', () {
       if(AudioContext.supported) {
         var completer = new Completer<bool>();
         var context = new AudioContext();
         var scriptProcessor = context.createScriptProcessor(1024, 1, 2);
         scriptProcessor.connect(context.destination, 0, 0);
         bool alreadyCalled = false;
         scriptProcessor.onAudioProcess.listen((event) {
           if (!alreadyCalled) {
             completer.complete(true);
           }
           alreadyCalled = true;
         });
         return completer.future;
       }
     });
   });
 }