Remove old isolate API and update all code in the repository to use

tests/isolate/compute_this_script_browser_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.
 
 // Test that spawn works even when there are many script files in the page.
 // This requires computing correctly the URL to the orignal script, so we can
 // pass it to the web worker APIs.
 #library('compute_this_script');
 
 #import('dart:html');
@@ skipping 17 matching lines @@
     ReceivePort port = new ReceivePort();
     port.receive(expectAsync2((msg, _) {
       expect(msg, equals('re: hi'));
       port.close();
     }));
 
     SendPort s = spawnFunction(child);
     s.send('hi', port.toSendPort());
   });
 }