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

chrome/browser/dom_ui/options/advanced_options_handler.cc

Index: chrome/browser/dom_ui/options/advanced_options_handler.cc
diff --git a/chrome/browser/dom_ui/options/advanced_options_handler.cc b/chrome/browser/dom_ui/options/advanced_options_handler.cc
index dcbcb84b92d38b0483e7d77d846eba54fe23e23b..218a1b11e64e27fb39d482d1b694e4aadffa8abd 100644
--- a/chrome/browser/dom_ui/options/advanced_options_handler.cc
+++ b/chrome/browser/dom_ui/options/advanced_options_handler.cc
@@ -575,10 +575,10 @@ void AdvancedOptionsHandler::SetupProxySettingsSection() {
   // Disable the button if proxy settings are managed by a sysadmin or
   // overridden by an extension.
   PrefService* pref_service = dom_ui_->GetProfile()->GetPrefs();
-  const PrefService::Preference* proxy_server =
-      pref_service->FindPreference(prefs::kProxyServer);
-  bool is_extension_controlled = (proxy_server &&
-                                  proxy_server->IsExtensionControlled());
+  const PrefService::Preference* proxy_config =
+      pref_service->FindPreference(prefs::kProxy);
+  bool is_extension_controlled = (proxy_config &&
+                                  proxy_config->IsExtensionControlled());
 
   FundamentalValue disabled(proxy_prefs_->IsManaged() ||
                             is_extension_controlled);