Make includeAncestors match a separate method.

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

Index: tools/dom/templates/html/impl/impl_Element.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_Element.darttemplate b/tools/dom/templates/html/impl/impl_Element.darttemplate
index 32fce298624f7e8a223e1eeec844be719d7d1fc8..501c9972f287def47dd5cd58dde7e29cdb864385 100644
--- a/tools/dom/templates/html/impl/impl_Element.darttemplate
+++ b/tools/dom/templates/html/impl/impl_Element.darttemplate
@@ -879,7 +879,7 @@ $if DART2JS
    * 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)) {
@@ -896,20 +896,14 @@ $if DART2JS
 $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;
   }