Make VM event streams look like real dart streams.

runtime/observatory/tests/service/debugger_location_test.dart

 // Copyright (c) 2015, 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 'package:observatory/service_io.dart';
 import 'package:observatory/debugger.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
 import 'dart:async';
@@ skipping 38 matching lines @@
   });
 }
 
 var tests = [
 
 // Bring the isolate to a breakpoint at line 15.
 (Isolate isolate) {
   return isolate.rootLibrary.load().then((_) {
       // Listen for breakpoint event.
       Completer completer = new Completer();
-      isolate.vm.events.stream.listen((ServiceEvent event) {
-        if (event.kind == ServiceEvent.kPauseBreakpoint) {
-          completer.complete();
-        }
+      isolate.vm.getEventStream(VM.kDebugStream).then((stream) {
+        var subscription;
+        subscription = stream.listen((ServiceEvent event) {
+          if (event.kind == ServiceEvent.kPauseBreakpoint) {
+            subscription.cancel();
+            completer.complete();
+          }
+        });
       });
 
       // Add the breakpoint.
       var script = isolate.rootLibrary.scripts[0];
       return isolate.addBreakpoint(script, 15).then((ServiceObject bpt) {
           return completer.future;  // Wait for breakpoint events.
       });
     });
 },
 
@@ skipping 199 matching lines @@
     return DebuggerLocation.complete(debugger, 'DebuggerLocationTestFoo.q')
       .then((List<String> completions) {
         expect(completions.toString(), equals('[]'));
       });
   });
 },
 
 ];
 
 main(args) => runIsolateTests(args, tests, testeeConcurrent: testFunction);