Reuse existing object proxies and exported objects, if these exist.

dbus/dbus.gyp

 # Copyright (c) 2011 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     {
@@ skipping 19 matching lines @@
       'target_name': 'dbus_unittests',
       'type': 'executable',
       'dependencies': [
         'dbus',
         '../base/base.gyp:test_support_base',
         '../testing/gtest.gyp:gtest',
         '../build/linux/system.gyp:dbus',
       ],
       'sources': [
         '../base/test/run_all_unittests.cc',
+        'bus_unittest.cc',
         'message_unittest.cc',
         'end_to_end_async_unittest.cc',
         'end_to_end_sync_unittest.cc',
         'test_service.cc',
         'test_service.h',
       ],
       'include_dirs': [
         '..',
       ],
     },
   ],
 }