Make VM event streams look like real dart streams.

runtime/observatory/tests/service/break_on_activation_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:unittest/unittest.dart';
 import 'test_helper.dart';
 
 genRepeater(value) {
@@ skipping 36 matching lines @@
   r3_named(y: 'Not a closure', x: 'Not a closure');
 }
 
 
 var tests = [
 (Isolate isolate) async {
   var rootLib = await isolate.rootLibrary.load();
 
   var breaksHit = 0;
 
-  var subscription;
-  subscription = isolate.vm.events.stream.listen((ServiceEvent event) {
-    if (event.kind == ServiceEvent.kPauseBreakpoint) {
-      print("Hit breakpoint ${event.breakpoint}");
-      breaksHit++;
-      isolate.resume();
-    }
-  });
+  var subscriptionFuture = isolate.vm.listenEventStream(
+      VM.kDebugStream, (ServiceEvent event) {
+        if (event.kind == ServiceEvent.kPauseBreakpoint) {
+          print("Hit breakpoint ${event.breakpoint}");
+          breaksHit++;
+          isolate.resume();
+        }
+      });
 
   valueOfField(String name) async {
     var field = rootLib.variables.singleWhere((v) => v.name == name);
     await field.load();
     return field.staticValue;
 
   }
   var r1Ref = await valueOfField('r1');
 
   var bpt1 = await isolate.addBreakOnActivation(r1Ref);
   print("Added breakpoint $bpt1");
   expect(bpt1 is Breakpoint, isTrue);
   expect(breaksHit, equals(0));
   await r1Ref.reload();
   expect(r1Ref.activationBreakpoint, equals(bpt1));
   print("testeeDo()");
   var res = await rootLib.evaluate("testeeDo()");
   expect(res is Instance, isTrue); // Not error.
   expect(breaksHit, equals(1));
 
   await isolate.removeBreakpoint(bpt1);
   print("Removed breakpoint $bpt1");
   print("testeeDo()");
   await r1Ref.reload();
   expect(r1Ref.activationBreakpoint, equals(null));
   res = await rootLib.evaluate("testeeDo()");
   expect(res is Instance, isTrue); // Not error.
   expect(breaksHit, equals(1));
 
-  await subscription.cancel();
+  await cancelFutureSubscription(subscriptionFuture);
 },
 
 (Isolate isolate) async {
   var rootLib = await isolate.rootLibrary.load();
 
   var breaksHit = 0;
 
-  var subscription;
-  subscription = isolate.vm.events.stream.listen((ServiceEvent event) {
-    if (event.kind == ServiceEvent.kPauseBreakpoint) {
-      print("Hit breakpoint ${event.breakpoint}");
-      breaksHit++;
-      isolate.resume();
-    }
-  });
+  var subscriptionFuture = isolate.vm.listenEventStream(
+      VM.kDebugStream, (ServiceEvent event) {
+        if (event.kind == ServiceEvent.kPauseBreakpoint) {
+          print("Hit breakpoint ${event.breakpoint}");
+          breaksHit++;
+          isolate.resume();
+        }
+      });
 
   valueOfField(String name) async {
     var field = rootLib.variables.singleWhere((v) => v.name == name);
     await field.load();
     return field.staticValue;
   }
   var r1Ref = await valueOfField('r1_named');
 
   var bpt1 = await isolate.addBreakOnActivation(r1Ref);
   print("Added breakpoint $bpt1");
   expect(bpt1 is Breakpoint, isTrue);
   expect(breaksHit, equals(0));
   await r1Ref.reload();
   expect(r1Ref.activationBreakpoint, equals(bpt1));
   print("testeeDoNamed()");
   var res = await rootLib.evaluate("testeeDoNamed()");
   expect(res is Instance, isTrue); // Not error.
   expect(breaksHit, equals(1));
 
   await isolate.removeBreakpoint(bpt1);
   print("Removed breakpoint $bpt1");
   await r1Ref.reload();
   expect(r1Ref.activationBreakpoint, equals(null));
   print("testeeDoNamed()");
   res = await rootLib.evaluate("testeeDoNamed()");
   expect(res is Instance, isTrue); // Not error.
   expect(breaksHit, equals(1));
 
-  await subscription.cancel();
+  await cancelFutureSubscription(subscriptionFuture);
 },
 
 (Isolate isolate) async {
   var rootLib = await isolate.rootLibrary.load();
 
   var breaksHit = 0;
 
-  var subscription;
-  subscription = isolate.vm.events.stream.listen((ServiceEvent event) {
-    if (event.kind == ServiceEvent.kPauseBreakpoint) {
-      print("Hit breakpoint ${event.breakpoint}");
-      breaksHit++;
-      isolate.resume();
-    }
-  });
+  var subscriptionFuture = isolate.vm.listenEventStream(
+      VM.kDebugStream, (ServiceEvent event) {
+        if (event.kind == ServiceEvent.kPauseBreakpoint) {
+          print("Hit breakpoint ${event.breakpoint}");
+          breaksHit++;
+          isolate.resume();
+        }
+      });
 
   valueOfField(String name) async {
     var field = rootLib.variables.singleWhere((v) => v.name == name);
     await field.load();
     return field.staticValue;
   }
   var r1Ref = await valueOfField('r1');
   var r2Ref = await valueOfField('r2');
 
   var bpt1 = await isolate.addBreakOnActivation(r1Ref);
@@ skipping 29 matching lines @@
 
   await isolate.removeBreakpoint(bpt2);
   print("Removed breakpoint $bpt2");
   await r2Ref.reload();
   expect(r2Ref.activationBreakpoint, equals(null));
   print("testeeDo()");
   res = await rootLib.evaluate("testeeDo()");
   expect(res is Instance, isTrue); // Not error.
   expect(breaksHit, equals(4));
 
-  await subscription.cancel();
+  await cancelFutureSubscription(subscriptionFuture);
 },
 
 ];
 
 main(args) => runIsolateTests(args, tests, testeeBefore: testeeSetup);