Add a CallbackRegistry class to base/ to manage callbacks

base/base.gyp

 # Copyright (c) 2012 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,
   },
   'includes': [
     '../build/win_precompile.gypi',
@@ skipping 437 matching lines @@
         'android/path_utils_unittest.cc',
         'android/scoped_java_ref_unittest.cc',
         'at_exit_unittest.cc',
         'atomicops_unittest.cc',
         'base64_unittest.cc',
         'bind_helpers_unittest.cc',
         'bind_unittest.cc',
         'bind_unittest.nc',
         'bits_unittest.cc',
         'build_time_unittest.cc',
+        'callback_list_unittest.cc',
         'callback_unittest.cc',
         'callback_unittest.nc',
         'cancelable_callback_unittest.cc',
         'command_line_unittest.cc',
         'containers/hash_tables_unittest.cc',
         'containers/linked_list_unittest.cc',
         'containers/mru_cache_unittest.cc',
         'containers/small_map_unittest.cc',
         'containers/stack_container_unittest.cc',
         'cpu_unittest.cc',
@@ skipping 838 matching lines @@
             'base_unittests.isolate',
           ],
           'sources': [
             'base_unittests.isolate',
           ],
         },
       ],
     }],
   ],
 }