Make proxy settings one atomic dictionary in the PrefStores such that modifications are atomic.

chrome/chrome_browser.gypi

 # Copyright (c) 2011 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': [
     {
       'target_name': 'browser',
       'type': '<(library)',
       'msvs_guid': '5BF908A7-68FB-4A4B-99E3-8C749F1FE4EA',
@@ skipping 1812 matching lines @@
         'browser/prefs/pref_notifier_impl.cc',
         'browser/prefs/pref_notifier_impl.h',
         'browser/prefs/pref_service.cc',
         'browser/prefs/pref_service.h',
         'browser/prefs/pref_set_observer.cc',
         'browser/prefs/pref_set_observer.h',
         'browser/prefs/pref_value_map.cc',
         'browser/prefs/pref_value_map.h',
         'browser/prefs/pref_value_store.cc',
         'browser/prefs/pref_value_store.h',
+        'browser/prefs/proxy_config_dictionary.cc',
+        'browser/prefs/proxy_config_dictionary.h',
         'browser/prefs/proxy_prefs.cc',
         'browser/prefs/proxy_prefs.h',
         'browser/prefs/scoped_pref_update.cc',
         'browser/prefs/scoped_pref_update.h',
         'browser/prefs/session_startup_pref.cc',
         'browser/prefs/session_startup_pref.h',
         'browser/prefs/value_map_pref_store.cc',
         'browser/prefs/value_map_pref_store.h',
         'browser/prerender/prerender_contents.cc',
         'browser/prerender/prerender_contents.h',
@@ skipping 2757 matching lines @@
       ],
     },
   ],
 }
 
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