Adding debugging output to flaky tests to help diagnose problems on the bots.

runtime/observatory/tests/service/pause_on_start_and_exit_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=--error_on_bad_type --error_on_bad_override
 
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
 import 'dart:async';
 
 void testMain() {
   print('Hello');
 }
 
 var tests = [
 
 (Isolate isolate) async {
+  print('Getting stream...');
   Completer completer = new Completer();
   var stream = await isolate.vm.getEventStream(VM.kDebugStream);
+  print('Subscribing...');
   var subscription;
   subscription = stream.listen((ServiceEvent event) {
     if (event.kind == ServiceEvent.kPauseStart) {
-      print('Received PauseStart');
+      print('Received $event');
       subscription.cancel();
       completer.complete();
+    } else {
+      print('Ignoring event $event');
     }
   });
+  print('Subscribed.  Pause event is ${isolate.pauseEvent}');
 
   if (isolate.pauseEvent != null &&
       isolate.pauseEvent.kind == ServiceEvent.kPauseStart) {
     // Wait for the isolate to hit PauseStart.
     subscription.cancel();
+    print('Subscription cancelled.');
   } else {
+    print('Waiting for pause start event.');
     await completer.future;
   }
+  print('Done waiting for pause event.');
 
   // Grab the timestamp.
   var pausetime1 = isolate.pauseEvent.timestamp;
   expect(pausetime1, isNotNull);
   // Reload the isolate.
   await isolate.reload();
   // Verify that it is the same.
   expect(pausetime1.millisecondsSinceEpoch,
          equals(isolate.pauseEvent.timestamp.millisecondsSinceEpoch));
 
@@ skipping 23 matching lines @@
          equals(isolate.pauseEvent.timestamp.millisecondsSinceEpoch));
   expect(pausetime2.millisecondsSinceEpoch,
          greaterThan(pausetime1.millisecondsSinceEpoch));
 },
 
 ];
 
 main(args) => runIsolateTests(args, tests,
                               testeeConcurrent: testMain,
                               pause_on_start: true, pause_on_exit: true);