Cleanups in collection.

tests/corelib/collection_length_test.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 map_test;
 import 'dart:collection';
 
 // Test that length/isEmpty opertions are constant time on
 // maps, strings and collections.
 
@@ skipping 23 matching lines @@
 }
 
 void testCollection(Collection collection, n) {
   for (int i = 0; i < n; i++) {
     collection.add(i);
   }
   testLength(collection, n);
 }
 
 void testList(List list, n) {
+  // Works even if list is fixed-length.
   for (int i = 0; i < n; i++) {
     list[i] = i;
   }
   testLength(list, n);
 }
 
 
 void testLength(var lengthable, int size) {
   print(lengthable.runtimeType);  // Show what hangs the test.
   int length = 0;
   // If length or isEmpty is not a constant-time (or very fast) operation,
   // this will timeout.
   for (int i = 0; i < 100000; i++) {
     if (!lengthable.isEmpty) length += lengthable.length;
   }
   if (length != size * 100000) throw "Bad length: $length / size: $size";
 }
 
 
 main() {
   const int N = 100000;
   testMap(new HashMap(), N);
   testMap(new LinkedHashMap(), N);
   testMap(new SplayTreeMap(), N);
   testCollection(new HashSet(), N);
   testCollection(new LinkedHashSet(), N);
   testCollection(new ListQueue(), N);
+  testCollection(new DoubleLinkedQueue(), N);
   testList(new List()..length = N, N);
   testList(new List(N), N);
   testString(N);
-  // DoubleLinkedQueue has linear length, but fast isEmpty.
 }