Fix a race condition in preference metric reporting.

chrome/chrome_tests_unit.gypi

 # Copyright 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.
 {
   'targets': [
     {
       # This target contains mocks and test utilities that don't belong in
       # production libraries but are used by more than one test executable.
       'target_name': 'test_support_common',
       'type': 'static_library',
@@ skipping 1091 matching lines @@
         'browser/policy/url_blacklist_manager_unittest.cc',
         'browser/policy/url_blacklist_policy_handler_unittest.cc',
         'browser/predictors/autocomplete_action_predictor_table_unittest.cc',
         'browser/predictors/autocomplete_action_predictor_unittest.cc',
         'browser/predictors/resource_prefetch_predictor_unittest.cc',
         'browser/predictors/resource_prefetch_predictor_tables_unittest.cc',
         'browser/predictors/resource_prefetcher_unittest.cc',
         'browser/prefs/chrome_pref_service_unittest.cc',
         'browser/prefs/command_line_pref_store_unittest.cc',
         'browser/prefs/incognito_mode_prefs_unittest.cc',
-        'browser/prefs/pref_metrics_service_unittest.cc',
+        'browser/prefs/pref_hash_calculator_unittest.cc',
+        'browser/prefs/pref_hash_filter_unittest.cc',
+        'browser/prefs/pref_hash_store_impl_unittest.cc',
         'browser/prefs/pref_model_associator_unittest.cc',
         'browser/prefs/proxy_config_dictionary_unittest.cc',
         'browser/prefs/proxy_policy_unittest.cc',
         'browser/prefs/proxy_prefs_unittest.cc',
         'browser/prefs/session_startup_pref_unittest.cc',
         'browser/prerender/prerender_history_unittest.cc',
         'browser/prerender/prerender_manager_unittest.cc',
         'browser/prerender/prerender_tracker_unittest.cc',
         'browser/prerender/prerender_unittest.cc',
         'browser/prerender/prerender_util_unittest.cc',
@@ skipping 1773 matching lines @@
             'browser/ui/app_list/test/fake_profile_store.cc',
             'browser/ui/app_list/test/fake_profile_store.h',
             'browser/ui/app_list/test/fast_show_pickler_unittest.cc',
             'browser/ui/views/app_list/win/app_list_win_unittest.cc',
           ],
         },
       ],
     }],
   ],  # 'conditions'
 }