Fix bug in DoubleLinkedQueue where removing from empty queue throws.

tests/corelib/queue_test.dart

 // Copyright (c) 2011, 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 queue.test;
 
 import "package:expect/expect.dart";
 import 'dart:collection';
 
 abstract class QueueTest {
@@ skipping 219 matching lines @@
 
     queue.removeWhere((x) => x == 7);
     testLength(26, queue);
 
     queue.retainWhere((x) => x != 3);
     testLength(23, queue);
 
     Expect.listEquals(
         [6, 8, 9, 1, 2, 4, 5, 6, 8, 9, 10, 1, 2, 4, 5, 6, 8, 9, 10, 1, 2, 4, 5],
         queue.toList());
+
+    // Regression test: http://dartbug.com/16270
+    // These should all do nothing, and should not throw.
+    Queue emptyQueue = newQueue();
+    emptyQueue.remove(0);
+    emptyQueue.removeWhere((x) => null);
+    emptyQueue.retainWhere((x) => null);
   }
 
   void testLarge() {
     int N = 10000;
     Set set = new Set();
 
     Queue queue = newQueue();
     Expect.isTrue(queue.isEmpty);
 
     for (int i = 0; i < N; i++) {
@@ skipping 151 matching lines @@
     }
     Expect.equals(null, entry2);
   }
 }
 
 
 main() {
   new DoubleLinkedQueueTest().testMain();
   new ListQueueTest().testMain();
 }