Adding a test to cover XCode UID collisions.

test/mac/duplicate-names/test.gyp

Index: test/mac/duplicate-names/test.gyp
===================================================================
--- test/mac/duplicate-names/test.gyp	(revision 0)
+++ test/mac/duplicate-names/test.gyp	(revision 0)
@@ -0,0 +1,15 @@
+# Copyright (c) 2012 Google Inc. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+{
+  'targets': [
+    {
+      'target_name': 'duplicate_names',
+      'type': 'shared_library',
+      'dependencies': [
+        'one/sub.gyp:one',
+        'two/sub.gyp:two',
+      ],
+    },
+  ],
+}