Adding tests for Element & Node lists insert method.

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 73 matching lines @@
     }
   }
 
   void insert(int index, Node node) {
     if (index < 0 || index > length) {
       throw new RangeError.range(index, 0, length);
     }
     if (index == length) {
       _this.append(node);
     } else {
-      this_.insertBefore(node, this[index]);
+      _this.insertBefore(node, this[index]);
     }
   }
 
   Node removeLast() {
     final result = last;
     if (result != null) {
       _this.$dom_removeChild(result);
     }
     return result;
   }
@@ skipping 220 matching lines @@
       }
     } else {
       for (var node in newNodes) {
         this.insertBefore(node, refChild);
       }
     }
   }
 
 $!MEMBERS
 }