New API to copy syncfs folder to localfs.

chrome/renderer/resources/extensions/developer_private_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 binding for the developerPrivate API.
+
+var binding = require('binding').Binding.create('developerPrivate');
+
+binding.registerCustomHook(function(bindingsAPI) {
+  var apiFunctions = bindingsAPI.apiFunctions;
+
+  // Converts the argument of |functionName| from DirectoryEntry to URL.
+  function bindFileSystemFunction(functionName) {
+    apiFunctions.setUpdateArgumentsPostValidate(
+        functionName, function(directoryEntry, callback) {
+          // toURL returns non-empty strings for syncfs directories.
+          if (directoryEntry.toURL() != "")
+            return [directoryEntry.toURL(), callback];
+          else
+            return [directoryEntry.fullPath, callback];
+    });
+  }
+
+  bindFileSystemFunction('loadDirectory');
+
+});
+
+exports.binding = binding.generate();