Add histograms to track synced pref changes.

chrome/chrome_tests.gypi

 # Copyright 2013 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' : {
     'pyautolib_sources': [
       'app/chrome_command_ids.h',
       'app/chrome_dll_resource.h',
       'common/automation_constants.h',
       'common/pref_names.cc',
@@ skipping 1465 matching lines @@
         'browser/policy/cloud/test_request_interceptor.cc',
         'browser/policy/cloud/test_request_interceptor.h',
         'browser/policy/mock_policy_service.cc',
         'browser/policy/mock_policy_service.h',
         'browser/policy/policy_browsertest.cc',
         'browser/policy/policy_prefs_browsertest.cc',
         'browser/policy/test_utils.cc',
         'browser/policy/test_utils.h',
         'browser/prefs/pref_functional_browsertest.cc',
         'browser/prefs/pref_service_browsertest.cc',
+        'browser/prefs/synced_pref_change_registrar_browsertest.cc',
         'browser/prerender/prefetch_browsertest.cc',
         'browser/prerender/prerender_browsertest.cc',
         'browser/printing/cloud_print/test/cloud_print_policy_browsertest.cc',
         'browser/printing/cloud_print/test/cloud_print_proxy_process_browsertest.cc',
         'browser/printing/print_preview_dialog_controller_browsertest.cc',
         'browser/printing/printing_layout_browsertest.cc',
         'browser/process_singleton_browsertest.cc',
         'browser/profiles/avatar_menu_model_browsertest.cc',
         'browser/profiles/profile_browsertest.cc',
         'browser/profiles/profile_manager_browsertest.cc',
@@ skipping 1899 matching lines @@
             'utility',
           ],
           'sources': [
             'tools/service_discovery_sniffer/service_discovery_sniffer.h',
             'tools/service_discovery_sniffer/service_discovery_sniffer.cc',
           ],
         }]
     }],
   ],  # 'conditions'
 }