Remember when an isolate was paused and subtly display it in Obseravatory

runtime/observatory/tests/service/pause_on_start_then_step_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 {
@@ skipping 11 matching lines @@
   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;
   }
 
+  // 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));
+
   completer = new Completer();
   stream = await isolate.vm.getEventStream(VM.kDebugStream);
   subscription = stream.listen((ServiceEvent event) {
     if (event.kind == ServiceEvent.kPauseBreakpoint) {
       print('Received PauseBreakpoint');
       subscription.cancel();
       completer.complete();
     }
     print('Got ${event.kind}');
   });
 
   print('Stepping...');
   isolate.stepInto();
 
   // Wait for the isolate to hit PauseBreakpoint.
   print('Waiting for PauseBreakpoint');
   await completer.future;
+
+  // Grab the timestamp.
+  var pausetime2 = isolate.pauseEvent.timestamp;
+  expect(pausetime2, isNotNull);
+  // Reload the isolate.
+  await isolate.reload();
+  // Verify that it is the same.
+  expect(pausetime2.millisecondsSinceEpoch,
+         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);