Add "last" setter to List.

pkg/third_party/html5lib/lib/src/list_proxy.dart

 // TODO(jmesserly): remove this once we have a subclassable growable list
 // in our libraries.
 
 /// A [List] proxy that you can subclass.
 library list_proxy;
 
 import 'dart:collection';
 import 'dart:math' show Random;
 
 // TOOD(jmesserly): this needs to be removed, but fixing NodeList is tricky.
@@ skipping 29 matching lines @@
 
   // From Iterable
   Iterator<E> get iterator => _list.iterator;
 
   // From List
   E operator [](int index) => _list[index];
   operator []=(int index, E value) { _list[index] = value; }
   set length(int value) { _list.length = value; }
   void add(E value) { _list.add(value); }
 
+  void set last(E value) { _list.last = value; }
   void addLast(E value) { add(value); }
   void addAll(Iterable<E> collection) { _list.addAll(collection); }
   void sort([int compare(E a, E b)]) { _list.sort(compare); }
   void shuffle([Random random]) { _list.shuffle(random); }
 
   int indexOf(E element, [int start = 0]) => _list.indexOf(element, start);
   int lastIndexOf(E element, [int start]) => _list.lastIndexOf(element, start);
   void clear() { _list.clear(); }
 
   E removeAt(int index) => _list.removeAt(index);
@@ skipping 19 matching lines @@
   Map<int, E> asMap() => _list.asMap();
 
   void replaceRange(int start, int end, Iterable<E> newContents) =>
       _list.replaceRange(start, end, newContents);
 
   void setAll(int index, Iterable<E> iterable) => _list.setAll(index, iterable);
 
   void fillRange(int start, int end, [E fillValue])
       => _list.fillRange(start, end, fillValue);
 }