Add mirrors tests for Null type.

tests/lib/mirrors/relation_subclass_test.dart

 // Copyright (c) 2014, 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.
 
 library test.relation_subclass;
 
 import "dart:mirrors";
 
 import "package:expect/expect.dart";
 
@@ skipping 10 matching lines @@
 typedef double DoubleGenerator();
 
 test(MirrorSystem mirrors) {
   LibraryMirror coreLibrary = mirrors.findLibrary(#dart.core);
   LibraryMirror thisLibrary = mirrors.findLibrary(#test.relation_subclass);
 
   ClassMirror Super = thisLibrary.declarations[#Superclass];
   ClassMirror Sub1 = thisLibrary.declarations[#Subclass1];
   ClassMirror Sub2 = thisLibrary.declarations[#Subclass2];
   ClassMirror Obj = coreLibrary.declarations[#Object];
+  ClassMirror Nul = coreLibrary.declarations[#Null];
 
   Expect.isTrue(Obj.isSubclassOf(Obj));
   Expect.isTrue(Super.isSubclassOf(Super));
   Expect.isTrue(Sub1.isSubclassOf(Sub1));
   Expect.isTrue(Sub2.isSubclassOf(Sub2));
+  Expect.isTrue(Nul.isSubclassOf(Nul));
 
   Expect.isTrue(Sub1.isSubclassOf(Super));
   Expect.isFalse(Super.isSubclassOf(Sub1));
 
   Expect.isTrue(Sub2.isSubclassOf(Super));
   Expect.isFalse(Super.isSubclassOf(Sub2));
 
   Expect.isFalse(Sub2.isSubclassOf(Sub1));
   Expect.isFalse(Sub1.isSubclassOf(Sub2));
 
   Expect.isTrue(Sub1.isSubclassOf(Obj));
   Expect.isFalse(Obj.isSubclassOf(Sub1));
 
   Expect.isTrue(Sub2.isSubclassOf(Obj));
   Expect.isFalse(Obj.isSubclassOf(Sub2));
 
   Expect.isTrue(Super.isSubclassOf(Obj));
   Expect.isFalse(Obj.isSubclassOf(Super));
 
+  Expect.isTrue(Nul.isSubclassOf(Obj));
+  Expect.isFalse(Obj.isSubclassOf(Nul));
+  Expect.isFalse(Nul.isSubclassOf(Super));
+  Expect.isFalse(Super.isSubclassOf(Nul));
+
   var Func = coreLibrary.declarations[#Function];
   Expect.isTrue(Func.isSubclassOf(Obj));
   Expect.isFalse(Obj.isSubclassOf(Func));
 
   // Function typedef.
   var NumPred = thisLibrary.declarations[#NumberPredicate];
   var IntPred = thisLibrary.declarations[#IntegerPredicate];
   var DubPred = thisLibrary.declarations[#DoublePredicate];
   var NumGen = thisLibrary.declarations[#NumberGenerator];
   var IntGen = thisLibrary.declarations[#IntegerGenerator];
@@ skipping 36 matching lines @@
   // IntPredRef.isSubclassOf(Func);
   // DubPredRef.isSubclassOf(Func);
   // NumGenRef.isSubclassOf(Func);
   // IntGenRef.isSubclassOf(Func);
   // DubGenRef.isSubclassOf(Func);
 }
 
 main() {
   test(currentMirrorSystem());
 }