Making ScriptProcessorNode not an EventTarget.

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';
+import 'dart:async';
 
 main() {
 
   useHtmlConfiguration();
 
   var isAudioContext =
       predicate((x) => x is AudioContext, 'is an AudioContext');
 
   test('constructorTest', () {
       var ctx = new AudioContext();
@@ skipping 18 matching lines @@
     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.createOscillator() is OscillatorNode, isTrue);
     expect(context.createPanner() is PannerNode, isTrue);
     expect(context.createScriptProcessor(4096) is ScriptProcessorNode, isTrue);
   });
+
+  test('onAudioProcess', () {
+    var context = new AudioContext();
+    var scriptProcessor = context.createScriptProcessor(1024, 1, 2);
+    scriptProcessor.connect(context.destination, 0, 0);
+    var completer = new Completer<bool>();
+    bool alreadyCalled = false;
+    scriptProcessor.onAudioProcess = (event) {
+      if (!alreadyCalled) {
+        completer.complete(true);
+      }
+      alreadyCalled = true;
+    };
+    return completer.future;
+  });
 }