Make VM event streams look like real dart streams.

runtime/observatory/tests/service/break_on_activation_test.dart

Index: runtime/observatory/tests/service/break_on_activation_test.dart
diff --git a/runtime/observatory/tests/service/break_on_activation_test.dart b/runtime/observatory/tests/service/break_on_activation_test.dart
index b26695406bf9bd99b17b1e6eb1f283aaafaecb82..c9cba58b4b958d37761a4f2215614855f004d887 100644
--- a/runtime/observatory/tests/service/break_on_activation_test.dart
+++ b/runtime/observatory/tests/service/break_on_activation_test.dart
@@ -54,13 +54,15 @@ var tests = [
 
   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;
+  subscriptionFuture = isolate.vm.getDebugEventStream().then((stream) {
+      return stream.listen((ServiceEvent event) {
+          if (event.kind == ServiceEvent.kPauseBreakpoint) {
+            print("Hit breakpoint ${event.breakpoint}");
+            breaksHit++;
+            isolate.resume();
+          }
+      });
   });
 
   valueOfField(String name) async {
@@ -91,7 +93,7 @@ var tests = [
   expect(res is Instance, isTrue); // Not error.
   expect(breaksHit, equals(1));
 
-  await subscription.cancel();
+  await (await subscriptionFuture).cancel();
 },
 
 (Isolate isolate) async {
@@ -99,13 +101,15 @@ var tests = [
 
   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;
+  subscriptionFuture = isolate.vm.getDebugEventStream().then((stream) {
+      return stream.listen((ServiceEvent event) {
+          if (event.kind == ServiceEvent.kPauseBreakpoint) {
+            print("Hit breakpoint ${event.breakpoint}");
+            breaksHit++;
+            isolate.resume();
+          }
+      });
   });
 
   valueOfField(String name) async {
@@ -135,7 +139,7 @@ var tests = [
   expect(res is Instance, isTrue); // Not error.
   expect(breaksHit, equals(1));
 
-  await subscription.cancel();
+  await (await subscriptionFuture).cancel();
 },
 
 (Isolate isolate) async {
@@ -143,13 +147,15 @@ var tests = [
 
   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;
+  subscriptionFuture = isolate.vm.getDebugEventStream().then((stream) {
+      return stream.listen((ServiceEvent event) {
+          if (event.kind == ServiceEvent.kPauseBreakpoint) {
+            print("Hit breakpoint ${event.breakpoint}");
+            breaksHit++;
+            isolate.resume();
+          }
+      });
   });
 
   valueOfField(String name) async {
@@ -200,7 +206,7 @@ var tests = [
   expect(res is Instance, isTrue); // Not error.
   expect(breaksHit, equals(4));
 
-  await subscription.cancel();
+  await (await subscriptionFuture).cancel();
 },
 
 ];