Revert "Remove NullPointerException."

pkg/unittest/test/matchers_test.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.
 
 library unittestTests;
 import '../../../pkg/unittest/lib/unittest.dart';
 part 'test_utils.dart';
 
 doesNotThrow() {}
 doesThrow() { throw 'X'; }
@@ skipping 137 matching lines @@
     test('throwsUnimplementedError', () {
       shouldPass(() { throw new UnimplementedError(''); },
           throwsUnimplementedError);
       shouldFail(() { throw new Exception(); },
           throwsUnimplementedError,
         "Expected: throws an exception which matches UnimplementedError "
         "but:  exception <Exception> does not match "
             "UnimplementedError.");
     });
 
+    test('throwsNullPointerException', () {
+      shouldPass(() { throw new NullPointerException(''); },
+          throwsNullPointerException);
+      shouldFail(() { throw new Exception(); },
+          throwsNullPointerException,
+        "Expected: throws an exception which matches NullPointerException "
+        "but:  exception <Exception> does not match "
+            "NullPointerException.");
+    });
+
     test('throwsUnsupportedError', () {
       shouldPass(() { throw new UnsupportedError(''); },
           throwsUnsupportedError);
       shouldFail(() { throw new Exception(); },
           throwsUnsupportedError,
         "Expected: throws an exception which matches UnsupportedError "
         "but:  exception <Exception> does not match "
             "UnsupportedError.");
     });
 
@@ skipping 359 matching lines @@
       var w = new Widget();
       w.price = 10;
       shouldPass(w, new HasPrice(greaterThan(0)));
       shouldFail(w, new HasPrice(greaterThan(10)),
           'Expected: Widget with a price that is a value greater than <10> '
           'but: price was <10>.');
     });
   });
 }