Add the streamListen and streamCancel rpcs to the vm service.

runtime/observatory/tests/service/echo_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.
 // VMOptions=--compile-all --error_on_bad_type --error_on_bad_override
 
 import 'dart:async';
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
 
 var tests = [
 
 (Isolate isolate) =>
   isolate.vm.invokeRpc('_echo', { 'text': 'hello'}).then((result) {
     expect(result['type'], equals('_EchoResponse'));
     expect(result['text'], equals('hello'));
   }),
 
 (Isolate isolate) =>
   isolate.invokeRpc('_echo', { 'text': 'hello'}).then((result) {
     expect(result['type'], equals('_EchoResponse'));
     expect(result['text'], equals('hello'));
   }),
 
 (Isolate isolate) {
   Completer completer = new Completer();
-  isolate.vm.events.stream.listen((ServiceEvent event) {
+  isolate.vm.getEventStream('_Echo').listen((ServiceEvent event) {
     if (event.eventType == '_Echo') {
       expect(event.data.lengthInBytes, equals(3));
       expect(event.data.getUint8(0), equals(0));
       expect(event.data.getUint8(1), equals(128));
       expect(event.data.getUint8(2), equals(255));
       completer.complete();
     }
   });
   isolate.invokeRpc('_triggerEchoEvent', { 'text': 'hello' });
   return completer.future;
 },
 
 ];
 
 main(args) => runIsolateTests(args, tests);