Add a CallbackRegistry class to base/ to manage callbacks

base/base.gypi

 # 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.
 
 {
   'target_defaults': {
     'variables': {
       'base_target': 0,
     },
     'target_conditions': [
@@ skipping 87 matching lines @@
           'bind_helpers.h',
           'bind_internal.h',
           'bind_internal_win.h',
           'bits.h',
           'build_time.cc',
           'build_time.h',
           'callback.h',
           'callback_helpers.h',
           'callback_internal.cc',
           'callback_internal.h',
+          'callback_list.h',
           'cancelable_callback.h',
           'chromeos/chromeos_version.cc',
           'chromeos/chromeos_version.h',
           'command_line.cc',
           'command_line.h',
           'compiler_specific.h',
           'containers/hash_tables.h',
           'containers/linked_list.h',
           'containers/mru_cache.h',
           'containers/small_map.h',
@@ skipping 767 matching lines @@
           ['<(use_system_nspr)==1 and >(nacl_untrusted_build)==0', {
             'sources/': [
               ['exclude', '^third_party/nspr/'],
             ],
           }],
         ],
       }],
     ],
   },
 }