Changed UnsupportedOperationException to UnsupportedError

lib/dom.dart

 /**
  * A simple tree API that results from parsing html. Intended to be compatible
  * with dart:html, but right now it resembles the classic JS DOM.
  */
 library dom;
 
 import 'src/constants.dart';
 import 'src/list_proxy.dart';
 import 'src/treebuilder.dart';
 import 'src/utils.dart';
@@ skipping 467 matching lines @@
   void removeRange(int start, int rangeLength) {
     for (int i = start; i < rangeLength; i++) this[i].parent = null;
     super.removeRange(start, rangeLength);
   }
 
   void insertRange(int start, int rangeLength, [Node initialValue]) {
     if (initialValue == null) {
       throw new ArgumentError('cannot add null node.');
     }
     if (rangeLength > 1) {
-      throw new UnsupportedOperationException('cannot add the same node '
-          'multiple times.');
+      throw new UnsupportedError('cannot add the same node multiple times.');
     }
     super.insertRange(start, 1, _setParent(initialValue));
   }
 }