Revert "Remove NullPointerException."

pkg/unittest/test/matchers_test.dart

Index: pkg/unittest/test/matchers_test.dart
diff --git a/pkg/unittest/test/matchers_test.dart b/pkg/unittest/test/matchers_test.dart
index 81be8fbf22f91350c223cf5ec16e8f13c6278cba..c9045ad586688d9d96d2c38cba1971d2b1e21d30 100644
--- a/pkg/unittest/test/matchers_test.dart
+++ b/pkg/unittest/test/matchers_test.dart
@@ -155,6 +155,16 @@ void main() {
             "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);