Show nicer errors on some server failures.

utils/tests/pub/test_pub.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.
 
 /**
  * Test infrastructure for testing pub. Unlike typical unit tests, most pub
  * tests are integration tests that stage some stuff on the file system, run
  * pub, and then validate the results. This library provides an API to build
  * tests like that.
  */
@@ skipping 531 matching lines @@
 }
 
 Future<Directory> _setUpSandbox() {
   return createTempDir();
 }
 
 Future _runScheduled(Directory parentDir, List<_ScheduledEvent> scheduled) {
   if (scheduled == null) return new Future.immediate(null);
   var iterator = scheduled.iterator();
 
-  Future runNextEvent([_]) {
+  Future runNextEvent(_) {
     if (_abortScheduled || !iterator.hasNext()) {
       _abortScheduled = false;
       scheduled.clear();
       return new Future.immediate(null);
     }
 
     var future = iterator.next()(parentDir);
     if (future != null) {
       return future.chain(runNextEvent);
     } else {
-      return runNextEvent();
+      return runNextEvent(null);
     }
   }
 
-  return runNextEvent();
+  return runNextEvent(null);
 }
 
 /**
  * Compares the [actual] output from running pub with [expected]. For [String]
  * patterns, ignores leading and trailing whitespace differences and tries to
  * report the offending difference in a nice way. For other [Pattern]s, just
  * reports whether the output contained the pattern.
  */
 void _validateOutput(Pattern expected, List<String> actual) {
   if (expected == null) return;
@@ skipping 513 matching lines @@
 }
 
 /**
  * Schedules a callback to be called after Pub is run with [runPub], even if it
  * fails.
  */
 void _scheduleCleanup(_ScheduledEvent event) {
   if (_scheduledCleanup == null) _scheduledCleanup = [];
   _scheduledCleanup.add(event);
 }