Factor out PluginGroup into a separate class in common/.

chrome/chrome_common.gypi

 # Copyright (c) 2010 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': {
       'chrome_common_target': 0,
     },
     'target_conditions': [
@@ skipping 57 matching lines @@
           'common/nacl_types.h',
           'common/nacl_messages_internal.h',
           'common/notification_details.h',
           'common/notification_observer.h',
           'common/notification_registrar.cc',
           'common/notification_registrar.h',
           'common/notification_service.cc',
           'common/notification_service.h',
           'common/notification_source.h',
           'common/notification_type.h',
+          'common/plugin_group.cc',
+          'common/plugin_group.h',
           'common/process_watcher_mac.cc',
           'common/process_watcher_posix.cc',
           'common/process_watcher_win.cc',
           'common/process_watcher.h',
           'common/property_bag.cc',
           'common/property_bag.h',
           'common/ref_counted_util.h',
           'common/resource_response.h',
           'common/result_codes.h',
           'common/sandbox_init_wrapper.h',
@@ skipping 325 matching lines @@
           'configurations': {
             'Common_Base': {
               'msvs_target_platform': 'x64',
             },
           },
         },
       ],
     }],
   ],
 }