Add trace_service_pause_events flag and related tracing

tests/standalone/vmservice/test_helper.dart

 // Copyright (c) 2013, 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.
 
 library vmservice_test_helper;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 import 'package:expect/expect.dart';
@@ skipping 122 matching lines @@
     return Process.start(dartExecutable,
                          ['--enable-vm-service:0', scriptPath]).then((p) {
 
       Completer completer = new Completer();
       process = p;
       var portNumber;
       var blank;
       var first = true;
       process.stdout.transform(UTF8.decoder)
                     .transform(new LineSplitter()).listen((line) {
-        if (line.startsWith('VMService listening on ')) {
+        if (line.startsWith('Observatory listening on http://')) {
           RegExp portExp = new RegExp(r"\d+.\d+.\d+.\d+:(\d+)");
           var port = portExp.firstMatch(line).group(1);
           portNumber = int.parse(port);
         }
         if (line == '') {
           // Received blank line.
           blank = true;
         }
         if (portNumber != null && blank == true && first == true) {
           completer.complete(portNumber);
@@ skipping 112 matching lines @@
       });
     });
     return Future.wait(requests).then((a) {
       a.forEach((FieldRequestHelper field) {
         fields[field.field['user_name']] = field.field;
       });
       return this;
     });
   }
 }