Make 'where' lazy.

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;
 
 class QueueTest {
 
   static testMain() {
     Queue queue = new Queue();
@@ skipping 30 matching lines @@
       return (value == 10);
     }
 
     Queue mapped = new Queue.from(queue.mappedBy(mapTest));
     checkQueue(mapped, 3, 111);
     checkQueue(queue, 3, 1110);
     Expect.equals(1, mapped.removeFirst());
     Expect.equals(100, mapped.removeLast());
     Expect.equals(10, mapped.removeFirst());
 
-    Queue other = queue.where(is10);
+    Queue other = new Queue.from(queue.where(is10));
     checkQueue(other, 1, 10);
 
     Expect.equals(true, queue.some(is10));
 
     bool isInstanceOfInt(int value) {
       return (value is int);
     }
 
     Expect.equals(true, queue.every(isInstanceOfInt));
 
@@ skipping 29 matching lines @@
     queue.addFirst(2);
     Expect.equals(2, queue.first);
     Expect.equals(1, queue.last);
 
     queue.addLast(3);
     Expect.equals(3, queue.last);
     bool isGreaterThanOne(int value) {
       return (value > 1);
     }
 
-    other = queue.where(isGreaterThanOne);
+    other = new Queue.from(queue.where(isGreaterThanOne));
     checkQueue(other, 2, 5);
 
     testAddAll();
   }
 
   static void checkQueue(Queue queue, int expectedSize, int expectedSum) {
     Expect.equals(expectedSize, queue.length);
     int sum = 0;
     void sumElements(int value) {
       sum += value;
@@ skipping 65 matching lines @@
       entry1 = entry1.nextEntry();
       entry2 = entry2.nextEntry();
     }
     Expect.equals(null, entry2);
   }
 }
 
 main() {
   QueueTest.testMain();
 }