[Extensions] More bindings hardening

chrome/renderer/resources/extensions/platform_keys/get_public_key.js

 // Copyright 2015 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.
 
 var internalAPI = require('platformKeys.internalAPI');
 
 var normalizeAlgorithm =
     requireNative('platform_keys_natives').NormalizeAlgorithm;
 
 // Returns the normalized parameters of |importParams|.
@@ skipping 46 matching lines @@
       cert, importParams.name, function(publicKey, algorithm) {
         if (chrome.runtime.lastError) {
           callback();
           return;
         }
         var combinedAlgorithm = combineAlgorithms(algorithm, importParams);
         callback(publicKey, combinedAlgorithm);
       });
 }
 
-exports.getPublicKey = getPublicKey;
+exports.$set('getPublicKey', getPublicKey);