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

tools/dom/templates/html/impl/impl_Event.darttemplate

 // Copyright (c) 2012, 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.
 
 // WARNING: Do not edit - generated code.
 
 part of $LIBRARYNAME;
 
 $(ANNOTATIONS)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
   // In JS, canBubble and cancelable are technically required parameters to
@@ skipping 16 matching lines @@
    *
    *     var e = new Event.type('MouseEvent', 'mousedown', true, true);
    */
   factory Event.eventType(String type, String name, {bool canBubble: true,
       bool cancelable: true}) {
     final Event e = document._createEvent(type);
     e._initEvent(name, canBubble, cancelable);
     return e;
   }
 
-  $CLASSNAME._private();
+  /** 
+   * Caches the pointer to the element that matches CSS selector involved in
+   * the event.
+   */
+  Element _cachedMatchingTarget;

[blois, 2013/10/09 22:25:44]

Probably does not need to be cached- in most cases it's only called once.

Plus adding fields to native types in JS need more annotations I think.

[Emily Fortuna, 2013/10/09 22:39:18]

Removed

+  
+  /** The CSS selector involved with event delegation. */
+  String _selector;
+
+  /**
+   * A pointer to the element whose CSS selector matched within which an event
+   * was fired. If this Event was not associated with any Event delegation,
+   * then this value will be null.
+   */
+  Element matchingTarget() {

[blois, 2013/10/09 22:25:44]

Can this be a getter?

[Emily Fortuna, 2013/10/09 22:39:18]

Yeah, but it felt like a function was a little more appropriate since it does a
chunk of calculation beforehand. If you prefer I can switch it though.

[blois, 2013/10/09 23:12:57]

Yes plz! It just feels odd as a method when it's beside target and
currentTarget.

+    if (_cachedMatchingTarget == null) {
+      var currentTarget = this.currentTarget;
+      var target = this.target;
+      var matchedTarget;
+      while (matchedTarget == null && target != currentTarget && 
+          target != null) {
+        if (_selector != null && target.matches(_selector)) {

[blois, 2013/10/09 22:25:44]

Can there be an earlier out if _selector is null? Possibly even throw?

[Emily Fortuna, 2013/10/09 22:39:18]

added earlier out.

+          matchedTarget = target;
+        }
+        target = target.parent;
+      }
+      _cachedMatchingTarget = matchedTarget;
+    }
+    return _cachedMatchingTarget;
+  }
 $!MEMBERS
 }