Make List.remove return boolean.

tools/dom/templates/html/impl/impl_Node.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;
 
 /**
  * Lazy implementation of the child nodes of an element that does not request
  * the actual child nodes of an element until strictly necessary greatly
  * improving performance for the typical cases where it is not required.
@@ skipping 88 matching lines @@
   }
 
   Node removeAt(int index) {
     var result = this[index];
     if (result != null) {
       _this.$dom_removeChild(result);
     }
     return result;
   }
 
-  void remove(Object object) {
-    if (object is! Node) return;
+  bool remove(Object object) {
+    if (object is! Node) return false;
     Node node = object;
-    if (!identical(_this, node.parentNode)) return;
+    if (!identical(_this, node.parentNode)) return false;
     _this.$dom_removeChild(node);
+    return true;
   }
 
   void _filter(bool test(Node node), bool removeMatching) {
     // This implementation of removeWhere/retainWhere is more efficient
     // than the default in ListBase. Child nodes can be removed in constant
     // time.
     Node child = _this.$dom_firstChild;
     while (child != null) {
       Node nextChild = child.nextSibling;
       if (test(child) == removeMatching) {
@@ skipping 236 matching lines @@
   }
 
   /**
    * Print out a String representation of this Node.
    */
   String toString() => localName == null ?
       (nodeValue == null ? super.toString() : nodeValue) : localName;
 
 $!MEMBERS
 }