Remove race(s) in vmservice tests.

tests/standalone/vmservice/isolate_stacktrace_command_script.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 isolate_stacktrace_command_script;
 
 import 'dart:io';
 import 'dart:isolate';
 
 void a() {
   int x = 0;
+  print(''); // Print blank line to signal that we are ready.
   while (true) {
     x &= x;
   }
 }
 
 void b() {
   a();
 }
 
 class C {
   c() {
     b();
   }
 }
 
 void myIsolateName() {
   new C().c();
 }
 
 main() {
   spawnFunction(myIsolateName);
-  print(''); // Print blank line to signal that we are ready.
   // Wait until signaled from spawning test.
   stdin.first.then((_) => exit(0));
 }