Add the streamListen and streamCancel rpcs to the vm service.

runtime/observatory/tests/service/graph_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/object_graph.dart';
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
@@ skipping 21 matching lines @@
   // Larger than any other fixed-size list in a fresh heap.
   lst[1] = new List(123456);
 }
 
 int fooId;
 
 var tests = [
 
 (Isolate isolate) {
   Completer completer = new Completer();
-  isolate.vm.events.stream.listen((ServiceEvent event) {
+  isolate.vm.getEventStream('_Graph').listen((ServiceEvent event) {
     if (event.eventType == ServiceEvent.kGraph) {
       ReadStream reader = new ReadStream(event.data);
       ObjectGraph graph = new ObjectGraph(reader);
       expect(fooId, isNotNull);
       Iterable<ObjectVertex> foos = graph.vertices.where(
           (ObjectVertex obj) => obj.classId == fooId);
       expect(foos.length, equals(3));
       expect(foos.where(
           (ObjectVertex obj) => obj.succ.length == 0).length, equals(1));
       expect(foos.where(
@@ skipping 37 matching lines @@
     Class fooClass = lib.classes.first;
     fooId = fooClass.vmCid;
     isolate.invokeRpcNoUpgrade('requestHeapSnapshot', {});
     return completer.future;
   });
 },
 
 ];
 
 main(args) => runIsolateTests(args, tests, testeeBefore: script);