[Smart Lock] Expose the easy_unlock.proximity_required pref via the chrome.preferencesPrivate API.

chrome/browser/extensions/api/preference/chrome_direct_setting_api.cc

 // 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.
 
 #include "chrome/browser/extensions/api/preference/chrome_direct_setting_api.h"
 
 #include "base/bind.h"
 #include "base/containers/hash_tables.h"
 #include "base/lazy_instance.h"
 #include "base/prefs/pref_change_registrar.h"
@@ skipping 11 matching lines @@
     "types.private.ChromeDirectSetting.%s.onChange";
 
 class PreferenceWhitelist {
  public:
   PreferenceWhitelist() {
     whitelist_.insert("googlegeolocationaccess.enabled");
     whitelist_.insert("spdy_proxy.enabled");
     whitelist_.insert("data_reduction.daily_original_length");
     whitelist_.insert("data_reduction.daily_received_length");
     whitelist_.insert("data_reduction.update_daily_lengths");
+    whitelist_.insert("easy_unlock.proximity_required");
   }
 
   ~PreferenceWhitelist() {}
 
   bool IsPreferenceOnWhitelist(const std::string& pref_key){
     return whitelist_.find(pref_key) != whitelist_.end();
   }
 
   void RegisterEventListeners(
       Profile* profile,
@@ skipping 104 matching lines @@
         scoped_ptr<base::ListValue> args_copy(args.DeepCopy());
         scoped_ptr<Event> event(new Event(event_name, args_copy.Pass()));
         router->DispatchEventToExtension(extension_id, event.Pass());
       }
     }
   }
 }
 
 }  // namespace chromedirectsetting
 }  // namespace extensions