Revert "Add "last" setter to List."

tools/dom/src/ImmutableListMixin.dart

 // 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 dart.dom.html;
 
 abstract class ImmutableListMixin<E> implements List<E> {
   // From Iterable<$E>:
   Iterator<E> get iterator {
     // Note: NodeLists are not fixed size. And most probably length shouldn't
     // be cached in both iterator _and_ forEach method. For now caching it
     // for consistency.
     return new FixedSizeListIterator<E>(this);
   }
 
-  // From List<E>:
-  void set last(E value) {
-    throw new UnsupportedError("Cannot modify an immutable List.");
-  }
-
+  // From Collection<E>:
   void add(E value) {
     throw new UnsupportedError("Cannot add to immutable List.");
   }
 
   void addAll(Iterable<E> iterable) {
     throw new UnsupportedError("Cannot add to immutable List.");
   }
 
+  // From List<E>:
   void sort([int compare(E a, E b)]) {
     throw new UnsupportedError("Cannot sort immutable List.");
   }
 
   void shuffle([Random random]) {
     throw new UnsupportedError("Cannot shuffle immutable List.");
   }
 
   void insert(int index, E element) {
     throw new UnsupportedError("Cannot add to immutable List.");
@@ skipping 36 matching lines @@
   }
 
   void replaceRange(int start, int end, Iterable<E> iterable) {
     throw new UnsupportedError("Cannot modify an immutable List.");
   }
 
   void fillRange(int start, int end, [E fillValue]) {
     throw new UnsupportedError("Cannot modify an immutable List.");
   }
 }