Add "last" setter to List.

runtime/lib/typed_data.dart

Index: runtime/lib/typed_data.dart
diff --git a/runtime/lib/typed_data.dart b/runtime/lib/typed_data.dart
index b1845732b7df58203cae4084736826644c89f0e1..41c23bfc4dccde9f847e93e646c81cfbae638c33 100644
--- a/runtime/lib/typed_data.dart
+++ b/runtime/lib/typed_data.dart
@@ -409,6 +409,11 @@ abstract class _TypedListBase {
         "Cannot resize a fixed-length list");
   }
 
+  void set last(value) {
+    if (isEmpty) throw IterableElementError.noElement();
+    this[length - 1] = value;
+  }
+
   void add(value) {
     throw new UnsupportedError(
         "Cannot add to a fixed-length list");