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

chrome/common/extensions/api/preferences_private.json

 // 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.
 
 [
   {
     "namespace": "preferencesPrivate",
     "description": "none",
     "properties": {
+      "easyUnlockProximityRequired": {
+        "nocompile": true,
+        "$ref": "types.private.ChromeDirectSetting",
+        "value": ["easy_unlock.proximity_required", {"type":"boolean"}],
+        "description": "If true, a remote Easy Unlock device can only unlock the local device if it is in very close proximity (roughly, within a foot). This preference's value is a boolean, defaulting to <code>false</code>."
+      },
       "googleGeolocationAccessEnabled": {
         "nocompile": true,
         "$ref": "types.private.ChromeDirectSetting",
         "value": ["googlegeolocationaccess.enabled", {"type":"boolean"}],
         "description": "If enabled, Google services can access the user's location. This preference's value is a boolean, defaulting to <code>false</code>."
       },
       "spdyProxyEnabled": {
         "nocompile": true,
         "$ref": "types.private.ChromeDirectSetting",
         "value": ["spdy_proxy.enabled", {"type":"boolean"}],
@@ skipping 33 matching lines @@
                 "type": "array",
                 "items": {"type": "string"}
               }
             ]
           }
         ]
       }
     ]
   }
 ]