Deprecating Element.elements for Element.children.

tests/html/hidden_dom_1_test.dart

 library HiddenDom1Test;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 
 // Test that the dart:html API does not leak native jsdom methods:
 //   onfocus setter.
 
 main() {
   useHtmlConfiguration();
 
   test('test1', () {
-    document.body.elements.add(new Element.html(r'''
+    document.body.children.add(new Element.html(r'''
 <div id='div1'>
 Hello World!
 </div>'''));
     Element e = document.query('#div1');
     expect(e, isNotNull);
 
     checkNoSuchMethod(() { confuse(e).onfocus = null; });
   });
 
 }
@@ skipping 12 matching lines @@
   try {
     action();
   } catch (e) {
     ex = e;
   }
   if (ex == null)
     expect(false, isTrue, reason: 'Action should have thrown exception');
 
   expect(ex, isNoSuchMethodError);
 }