Simplify pause_idle_isolate_test and add more debugging output.

runtime/observatory/tests/service/service_test_common.dart

Index: runtime/observatory/tests/service/service_test_common.dart
diff --git a/runtime/observatory/tests/service/service_test_common.dart b/runtime/observatory/tests/service/service_test_common.dart
index 7435ee5c0fde984d2fe2fcf26e60c26971a94b91..872d994c547bdcc38032eab6ef9bdbe37ff4d638 100644
--- a/runtime/observatory/tests/service/service_test_common.dart
+++ b/runtime/observatory/tests/service/service_test_common.dart
@@ -88,10 +88,10 @@ Future<Isolate> hasPausedFor(Isolate isolate, String kind) {
     var subscription;
     subscription = stream.listen((ServiceEvent event) {
         if (event.kind == kind) {
-          print('Paused with $kind');
-          subscription.cancel();
           if (completer != null) {
             // Reload to update isolate.pauseEvent.
+            print('Paused with $kind');
+            subscription.cancel();
             completer.complete(isolate.reload());
             completer = null;
           }
@@ -103,9 +103,9 @@ Future<Isolate> hasPausedFor(Isolate isolate, String kind) {
       if ((isolate.pauseEvent != null) &&
          (isolate.pauseEvent.kind == kind)) {
         // Already waiting at a breakpoint.
-        print('Paused with $kind');
-        subscription.cancel();
         if (completer != null) {
+          print('Paused with $kind');
+          subscription.cancel();
           completer.complete(isolate);
           completer = null;
         }