Make includeAncestors match a separate method.

tools/dom/templates/html/impl/impl_Element.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.
 
 part of $LIBRARYNAME;
 
 class _ChildrenElementList extends ListBase<Element> {
   // Raw Element.
   final Element _element;
   final HtmlCollection _childElements;
@@ skipping 861 matching lines @@
         break;
       default:
         throw new ArgumentError("Invalid position ${where}");
     }
   }
 
   /**
    * Checks if this element matches the CSS selectors.
    */
   @Experimental()
-  bool _matches(String selectors) {
+  bool matches(String selectors) {
     if (JS('bool', '!!#.matches', this)) {
       return JS('bool', '#.matches(#)', this, selectors);
     } else if (JS('bool', '!!#.webkitMatchesSelector', this)) {
       return JS('bool', '#.webkitMatchesSelector(#)', this, selectors);
     } else if (JS('bool', '!!#.mozMatchesSelector', this)) {
       return JS('bool', '#.mozMatchesSelector(#)', this, selectors);
     } else if (JS('bool', '!!#.msMatchesSelector', this)) {
       return matches = JS('bool', '#.msMatchesSelector(#)', this, selectors);
     } else {
       throw new UnsupportedError("Not supported on this platform");
     }
     return false;
   }
 $else
 $endif
 
-  /**
-   * Checks if this element matches the CSS selectors.
-   *
-   * If `includeAncestors` is true, we examine all of this element's parent
-   * elements and also return true if any of its parent elements matches
-   * `selectors`.
-   */
+  /** Checks if this element or any of its parents match the CSS selectors. */
   @Experimental()
-  bool matches(String selectors, [includeAncestors = false]) {
+  bool matchesWithAncestors(String selectors) {
     var elem = this;
     do {
-      if (elem._matches(selectors)) return true;
+      if (elem.matches(selectors)) return true;
       elem = elem.parent;
-    } while(includeAncestors && elem != null);
+    } while(elem != null);
     return false;
   }
 
 $if DART2JS
   @Creates('Null')  // Set from Dart code; does not instantiate a native type.
 $endif
   Element _templateInstanceRef;
 
   // Note: only used if `this is! TemplateElement`
 $if DART2JS
@@ skipping 393 matching lines @@
   const ScrollAlignment._internal(this._value);
   toString() => 'ScrollAlignment.$_value';
 
   /// Attempt to align the element to the top of the scrollable area.
   static const TOP = const ScrollAlignment._internal('TOP');
   /// Attempt to center the element in the scrollable area.
   static const CENTER = const ScrollAlignment._internal('CENTER');
   /// Attempt to align the element to the bottom of the scrollable area.
   static const BOTTOM = const ScrollAlignment._internal('BOTTOM');
 }