Fix some failures in html/element_test by changing where(...)[0] to where(...).first.

tests/html/element_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 ElementTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_individual_config.dart';
 import 'dart:html';
 import 'dart:svg' as svg;
 
@@ skipping 41 matching lines @@
   var isBRElement = predicate((x) => x is BRElement, 'is a BRElement');
   var isInputElement =
       predicate((x) => x is InputElement, 'is an InputElement');
   var isImageElement =
       predicate((x) => x is ImageElement, 'is an ImageElement');
   var isSpanElement = predicate((x) => x is SpanElement, 'is a SpanElement');
   var isAnchorElement =
       predicate((x) => x is AnchorElement, 'is an AnchorElement');
   var isElementList =
       predicate((x) => x is List<Element>, 'is a List<Element>');
+  var isElementIterable =
+      predicate((x) => x is Iterable<Element>, 'is an Iterable<Element>');
   var isHeadingElement =
       predicate((x) => x is HeadingElement, 'is a HeadingElement');
 
   Element makeElement() => new Element.tag('div');
 
   Element makeElementWithChildren() =>
     new Element.html("<div><br/><img/><input/></div>");
 
   test('computedStyle', () {
     final element = document.body;
@@ skipping 293 matching lines @@
       el.children.forEach((n) => els.add(n));
       expect(els[0], isBRElement);
       expect(els[1], isImageElement);
       expect(els[2], isInputElement);
     });
 
     test('where', () {
       var filtered = makeElementWithChildren().children.
         where((n) => n is ImageElement);
       expect(1, filtered.length);
-      expect(filtered[0], isImageElement);
-      expect(filtered, isElementList);
+      expect(filtered.first, isImageElement);
+      expect(filtered, isElementIterable);
     });
 
     test('every', () {
       var el = makeElementWithChildren();
       expect(el.children.every((n) => n is Element), isTrue);
       expect(el.children.every((n) => n is InputElement), isFalse);
     });
 
     test('any', () {
       var el = makeElementWithChildren();
@@ skipping 199 matching lines @@
 
     testUnsupported('removeLast', () => getQueryAll().removeLast());
   });
 
   group('_ElementList', () {
     List<Element> makeElList() => makeElementWithChildren().children;
 
     test('where', () {
       var filtered = makeElList().where((n) => n is ImageElement);
       expect(filtered.length, 1);
-      expect(filtered[0], isImageElement);
-      expect(filtered, isElementList);
+      expect(filtered.first, isImageElement);
+      expect(filtered, isElementIterable);
     });
 
     test('getRange', () {
       var range = makeElList().getRange(1, 2);
       expect(range, isElementList);
       expect(range[0], isImageElement);
       expect(range[1], isInputElement);
     });
   });
 }