Make 'where' lazy.

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 765 matching lines @@
     // Special-case strings to support multi-level names like "myapp/packages".
     if (name is String) {
       var path = join(dir, name);
       return exists(path).chain((exists) {
         if (!exists) Expect.fail('File $name in $dir not found.');
         return validate(path);
       });
     }
 
     return listDir(dir).chain((files) {
-      var matches = files.where((file) => endsWithPattern(file, name));
-      if (matches.length == 0) {
+      var matches = files.where((file) => endsWithPattern(file, name)).toList();
+      if (matches.isEmpty) {
         Expect.fail('No files in $dir match pattern $name.');
       }
       if (matches.length == 1) return validate(matches[0]);
 
       var failures = [];
       var successes = 0;
       var completer = new Completer();
       checkComplete() {
         if (failures.length + successes != matches.length) return;
         if (successes > 0) {
@@ skipping 430 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);
 }