Make 'where' lazy.

tests/html/documentfragment_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 DocumentFragmentTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 part 'util.dart';
 
 main() {
   useHtmlConfiguration();
 
   var isAnchorElement =
       predicate((x) => x is AnchorElement, 'is an AnchorElement');
 
-  Collection<String> _nodeStrings(Collection<Node> input) {
+  List<String> _nodeStrings(Iterable<Node> input) {
     var out = new List<String>();
     for (Node n in input) {
       if (n is Element) {
         Element e = n;
         out.add(e.tagName);
       } else {
         out.add(n.text);
       }
     }
     return out;
@@ skipping 316 matching lines @@
   //   // assertConstError(() => fragment.classes.add('foo'));
   // });
 
   test('query searches the fragment', () {
     var fragment = new DocumentFragment.html(
       "<div class='foo'><a>foo</a><b>bar</b></div>");
     expect(fragment.query(".foo a").tagName, "A");
     expect(_nodeStrings(fragment.queryAll(".foo *")), equals(["A", "B"]));
   });
 }