When a font family pref changes to the empty string, pass it to WebKit.

chrome/chrome_tests.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.
 {
   'variables' : {
     'pyautolib_sources': [
       'app/chrome_command_ids.h',
       'app/chrome_dll_resource.h',
       'common/automation_constants.h',
       'common/pref_names.cc',
@@ skipping 2117 matching lines @@
         'common/mac/objc_method_swizzle_unittest.mm',
         'common/mac/objc_zombie_unittest.mm',
         'common/metrics/entropy_provider_unittest.cc',
         'common/metrics/metrics_log_base_unittest.cc',
         'common/metrics/metrics_log_manager_unittest.cc',
         'common/metrics/metrics_util_unittest.cc',
         'common/metrics/variations/variations_util_unittest.cc',
         'common/multi_process_lock_unittest.cc',
         'common/net/url_util_unittest.cc',
         'common/net/x509_certificate_model_unittest.cc',
+        'common/pref_names_util_unittest.cc',
         'common/service_process_util_unittest.cc',
         'common/switch_utils_unittest.cc',
         'common/thumbnail_score_unittest.cc',
         'common/time_format_unittest.cc',
         'common/web_apps_unittest.cc',
         'common/worker_thread_ticker_unittest.cc',
         'common/zip_reader_unittest.cc',
         'common/zip_unittest.cc',
         'nacl/nacl_ipc_adapter_unittest.cc',
         'nacl/nacl_validation_query_unittest.cc',
@@ skipping 2813 matching lines @@
             'sync_integration_tests.isolate',
           ],
           'sources': [
             'sync_integration_tests.isolate',
           ],
         },
       ],
     }],
   ],  # 'conditions'
 }