Fix a bug in overload dispatch.

tests/html/audiocontext_test.dart

 #library('AudioContextTest');
 #import('../../lib/unittest/unittest.dart');
 #import('../../lib/unittest/html_config.dart');
 #import('dart:html');
 
 main() {
 
   useHtmlConfiguration();
 
   test('constructorTest', () {
       var ctx = new AudioContext();
-      Expect.isTrue(ctx != null);
+      Expect.isNotNull(ctx);
       Expect.isTrue(ctx is AudioContext);
   });
+  test('createBuffer', () {
+      var ctx = new AudioContext();
+      ArrayBufferView arrayBufferView = new Float32Array.fromList([]);
+      try {
+        // Test that native overload is chosen correctly. Native implementation
+        // should throw 'SYNTAX_ERR' DOMException because the buffer is empty.
+        AudioBuffer buffer = ctx.createBuffer(arrayBufferView.buffer, false);
+      } catch(var e) {
+        Expect.equals(DOMException.SYNTAX_ERR, e.code);
+      }
+  });
 }