Add "last" setter to List.

pkg/third_party/html5lib/lib/dom.dart

 /// A simple tree API that results from parsing html. Intended to be compatible
 /// with dart:html, but it is missing many types and APIs.
 library dom;
 
 // TODO(jmesserly): lots to do here. Originally I wanted to generate this using
 // our Blink IDL generator, but another idea is to directly use the excellent
 // http://dom.spec.whatwg.org/ and http://html.spec.whatwg.org/ and just
 // implement that.
 
 import 'dart:collection';
@@ skipping 834 matching lines @@
     new List<Element>.from(_childNodes.where((n) => n is Element));
 
   void forEach(void f(Element element)) {
     _filtered.forEach(f);
   }
 
   void operator []=(int index, Element value) {
     this[index].replaceWith(value);
   }
 
+  void set last(Element value) {
+    this.last.replaceWith(value);
+  }
+
   void set length(int newLength) {
     final len = this.length;
     if (newLength >= len) {
       return;
     } else if (newLength < 0) {
       throw new ArgumentError("Invalid list length");
     }
 
     removeRange(newLength, len);
   }
@@ skipping 146 matching lines @@
 
 class _ConcatTextVisitor extends TreeVisitor {
   final _str = new StringBuffer();
 
   String toString() => _str.toString();
 
   visitText(Text node) {
     _str.write(node.data);
   }
 }