Add flag to disable capturing stack traces.

utils/tests/pub/update/git/update_to_nonexistent_pubspec_test.dart

 // Copyright (c) 2012, 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 pub_tests;
 
 import 'dart:io';
 
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
 main() {
+  initConfig();
   integration("updates Git packages to a nonexistent pubspec", () {
     ensureGit();
 
     var repo = d.git('foo.git', [
       d.libDir('foo'),
       d.libPubspec('foo', '1.0.0')
     ]);
     repo.create();
 
     d.appDir([{"git": "../foo.git"}]).create();
@@ skipping 15 matching lines @@
             r'pubspec.yaml file.'),
         exitCode: 1);
 
     d.dir(packagesPath, [
       d.dir('foo', [
         d.file('foo.dart', 'main() => "foo";')
       ])
     ]).validate();
   });
 }