Add test for Frog native class with same native name as interface.

tests/language/src/NativeLibrarySameNameUsedLib2.dart

+// Copyright (c) 2011, 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.
+
+// Native implementation.
+
+#library('lib2');
+#import('NativeLibrarySameNameUsedLib1.dart');  // To get interface I.
+
+// Native impl has same name as interface.
+class Impl implements I native "*I" {
+  Impl read() native;
+  write(Impl x) native;
+}