[Extensions] More bindings hardening

chrome/renderer/resources/extensions/downloads_custom_bindings.js

 // Copyright (c) 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.
 
 // Custom bindings for the downloads API.
 
 var binding = require('binding').Binding.create('downloads');
 var downloadsInternal = require('binding').Binding.create(
     'downloadsInternal').generate();
 var eventBindings = require('event_bindings');
@@ skipping 45 matching lines @@
                  results.results &&
                  (results.results.length != 0) &&
                  (results.results[0] === true));
     if (suggestable && !async)
       suggestCallback();
   } catch (e) {
     suggestCallback();
     throw e;
   }
 });
-exports.binding = binding.generate();
+exports.$set('binding', binding.generate());