Add "matchingTarget" function to Event, which is the Element that matched the CSS value selector.

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:async';
 import 'dart:html';
 import 'dart:svg' as svg;
@@ skipping 734 matching lines @@
     test('sublist', () {
       var range = makeElList().sublist(1, 3);
       expect(range, isElementList);
       expect(range[0], isImageElement);
       expect(range[1], isInputElement);
     });
   });
 
   group('eventDelegation', () {
     test('matches', () {
+      Element clickOne = new Element.a();
+      Element selectorOne = new Element.div()
+          ..classes.add('selector')
+          ..children.add(clickOne);
+
+      Element clickTwo = new Element.a();
+      Element selectorTwo = new Element.div()
+          ..classes.add('selector')
+          ..children.add(clickTwo);
+      document.body.append(selectorOne);
+      document.body.append(selectorTwo);
+
+      document.body.onClick.matches('.selector').listen(expectAsync1(
+          (Event event) {
+        expect(event.currentTarget, document.body);
+        expect(event.target, clickOne);
+        expect(event.matchingTarget, selectorOne);
+      }));
+      clickOne.click();
+
       Element elem = new Element.div()..classes.addAll(['a', 'b']);
       Element img = new Element.img()
         ..classes.addAll(['b', 'a', 'd'])
         ..id = 'cookie';
       Element input = new InputElement()..classes.addAll(['c', 'd']);
       var div = new Element.div()
         ..classes.add('a')
         ..id = 'wat';
       document.body.append(elem);
       document.body.append(img);
@@ skipping 130 matching lines @@
 
     test('sublist', () {
       var range = makeElementList().sublist(1, 3);
       expect(range.length, 2);
       expect(range[0], isBRElement);
       expect(range[1], isBRElement);
     });
 
   });
 }