Make the new JS interop test pass on Dartium.

tests/html/js_interop_2_test.dart

 // 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
 
 #library('JsInterop2Test');
 #import('../../lib/unittest/unittest.dart');
 #import('../../lib/unittest/html_config.dart');
 #import('dart:html');
 #import('dart:isolate');
 
 injectSource(code) {
   final script = new ScriptElement();
   script.type = 'text/javascript';
   script.innerHTML = code;
   document.body.nodes.add(script);
 }
 
-isolateTest = """
+var isolateTest = """
   function test(data) {
     if (data == 'sent')
       return 'received';
   }
 
   var port = new ReceivePortSync();
   port.receive(test);
   window.registerPort('test', port.toSendPort());
 """;
 
 main() {
   useHtmlConfiguration();
 
   test('isolateTest', () {
     injectSource(isolateTest);
 
     SendPortSync port = window.lookupPort('test');
     var result = port.callSync('sent');
     Expect.equals('received', result);
 
     result = port.callSync('ignore');
     Expect.isNull(result);
   });
 }