Major rework of vm service events.

runtime/observatory/test/gc_test.dart

 // Copyright (c) 2014, 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.
 
 import 'package:observatory/service_io.dart';
 import 'test_helper.dart';
 
 import 'dart:async';
 
 void script() {
   List<int> data;
   var grow;
   grow = (int iterations, int size, Duration duration) {
     if (iterations <= 0) {
       return;
     }
     data = new List<int>(size);
     new Timer(duration, () => grow(iterations - 1, size, duration));
   };
   grow(100, 1 << 24, new Duration(seconds: 1));
 }
 
 var tests = [
 
 (Isolate isolate) {
   Completer completer = new Completer();
   // Expect at least this many GC events.
   int gcCountdown = 3;
   isolate.vm.events.stream.listen((ServiceEvent event) {
-    if (event.eventType == 'GC' && --gcCountdown == 0) {
+    if (event.eventType == ServiceEvent.kGC && --gcCountdown == 0) {
       completer.complete();
     }
   });
   return completer.future;
 },
 
 ];
 
 main(args) => runIsolateTests(args, tests, testeeConcurrent: script);