Add List.insert.

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 65 matching lines @@
           _this.$dom_appendChild(iterable[0]);
         }
       }
       return;
     }
     for (Node node in iterable) {
       _this.$dom_appendChild(node);
     }
   }
 
+  void insertAt(int index, Node node) {
+    if (index < 0 || index > length) throw RangeError(index);
+    if (index == length) {
+      _this.$dom_appendChild(node);
+    } else {
+      throw new UnimplementedError("insertAt on NodeLists");
+    }
+  }
+
   Node removeLast() {
     final result = last;
     if (result != null) {
       _this.$dom_removeChild(result);
     }
     return result;
   }
 
   Node removeAt(int index) {
     var result = this[index];
@@ skipping 190 matching lines @@
       final Node parent = this.parentNode;
       parent.$dom_replaceChild(otherNode, this);
     } catch (e) {
 
     };
     return this;
   }
 
 $!MEMBERS
 }