Make VM event streams look like real dart streams.

runtime/observatory/tests/service/evaluate_activation_test.dart

Index: runtime/observatory/tests/service/evaluate_activation_test.dart
diff --git a/runtime/observatory/tests/service/evaluate_activation_test.dart b/runtime/observatory/tests/service/evaluate_activation_test.dart
index 7862026d596400658a44412b24e347a121f8d745..5dab9823d8896b6801b4efa173b22a4a35bcc6b2 100644
--- a/runtime/observatory/tests/service/evaluate_activation_test.dart
+++ b/runtime/observatory/tests/service/evaluate_activation_test.dart
@@ -78,8 +78,9 @@ testMethod(Isolate isolate) async {
   expect(bpt is Breakpoint, isTrue);  // I.e, not null.
 
   bool hitBreakpoint = false;
+  var stream = await isolate.vm.getDebugEventStream();
   var sub;
-  sub = isolate.vm.events.stream.listen((ServiceEvent event) async {
+  sub = stream.listen((ServiceEvent event) async {
     print("Event $event");
     if (event.kind == ServiceEvent.kPauseBreakpoint) {
       var frameNumber = 1, r;
@@ -126,8 +127,9 @@ testMethod2(Isolate isolate) async {
   expect(bpt is Breakpoint, isTrue);  // I.e, not null.
 
   bool hitBreakpoint = false;
+  var stream = await isolate.vm.getDebugEventStream();
   var sub;
-  sub = isolate.vm.events.stream.listen((ServiceEvent event) async {
+  sub = stream.listen((ServiceEvent event) async {
     print("Event $event");
     if (event.kind == ServiceEvent.kPauseBreakpoint) {
       var frameNumber = 1, r;
@@ -174,8 +176,9 @@ testMethod3(Isolate isolate) async {
   expect(bpt is Breakpoint, isTrue);  // I.e, not null.
 
   bool hitBreakpoint = false;
+  var stream = await isolate.vm.getDebugEventStream();
   var sub;
-  sub = isolate.vm.events.stream.listen((ServiceEvent event) async {
+  sub = stream.listen((ServiceEvent event) async {
     print("Event $event");
     if (event.kind == ServiceEvent.kPauseBreakpoint) {
       var frameNumber = 1, r;
@@ -215,8 +218,9 @@ testMethod4(Isolate isolate) async {
   expect(bpt is Breakpoint, isTrue);  // I.e, not null.
 
   bool hitBreakpoint = false;
+  var stream = await isolate.vm.getDebugEventStream();
   var sub;
-  sub = isolate.vm.events.stream.listen((ServiceEvent event) async {
+  sub = stream.listen((ServiceEvent event) async {
     print("Event $event");
     if (event.kind == ServiceEvent.kPauseBreakpoint) {
       var frameNumber = 1, r;