Ensure that hashCode and runtimeType work on null.

runtime/lib/object_patch.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.
 
 patch class Object {
 
   // Helpers used to implement hashCode. If a hashCode is used we remember it
   // using an Expando object. A new hashCode value is calculated using a Random
   // number generator.
   static Expando _hashCodeExp = new Expando("Object.hashCode");
   static Random _hashCodeRnd = new Random();
 
   /* patch */ int hashCode() {
     var result = _hashCodeExp[this];
     if (result == null) {
       result = _hashCodeRnd.nextInt(0x40000000);  // Stay in Smi range.
       _hashCodeExp[this] = result;
     }
     return result;
   }
 
   /* patch */ String toString() => _toString(this);
 
   /* patch */ Dynamic noSuchMethod(String functionName, List args) {
     _noSuchMethod(this, functionName, args);
   }
 
+  // Not yet supported.
+  /* patch */ Type get runtimeType => null;
+
   static void _noSuchMethod(Object obj, String functionName, List args)
       native "Object_noSuchMethod";
 
   static String _toString(Object obj) native "Object_toString";
 }