Create a dummy sandbox_unittests target on Mac.

sandbox/mac/sandbox_mac.gypi

+# Copyright 2014 The Chromium Authors. 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': 'sandbox_unittests',

[jln (very slow on Chromium), 2014/04/28 19:53:38]

When I added sandbox_linux_unittests it was strongly recommended to me to have
the "_linux_" in it to be able to treat it differently than the Windows ones.

Since you're relying on base/ for your main(), you might be ok sharing the name
with Windows, I don't have a strong opinion, troopers and infra folks would know
better.

+      'type': 'executable',
+      'sources': [
+        'temp_test.cc',
+      ],
+      'dependencies': [
+        '../base/base.gyp:base',
+        '../base/base.gyp:run_all_unittests',
+        '../testing/gtest.gyp:gtest',
+      ],
+      'include_dirs': [
+        '../',
+      ],
+    },
+  ],
+}