Add API to get a folder's size.

chrome/renderer/resources/extensions/file_manager_private_custom_bindings.js

 // Copyright (c) 2012 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 fileManagerPrivate API.
 
 // Bindings
 var binding = require('binding').Binding.create('fileManagerPrivate');
 var eventBindings = require('event_bindings');
 
@@ skipping 177 matching lines @@
     });
     fileManagerPrivateInternal.zipSelection(
         parentUrl, urls, destName, callback);
   });
 
   apiFunctions.setHandleRequest('validatePathNameLength', function(
         entry, name, callback) {
     var url = fileManagerPrivateNatives.GetEntryURL(entry);
     fileManagerPrivateInternal.validatePathNameLength(url, name, callback);
   });
+
+  apiFunctions.setHandleRequest('getDirectorySize', function(
+        entry, callback) {
+    var url = fileManagerPrivateNatives.GetEntryURL(entry);
+    fileManagerPrivateInternal.getDirectorySize(url, callback);
+  });
 });
 
 eventBindings.registerArgumentMassager(
     'fileManagerPrivate.onDirectoryChanged', function(args, dispatch) {
   // Convert the entry arguments into a real Entry object.
   args[0].entry = GetExternalFileEntry(args[0].entry);
   dispatch(args);
 });
 
 exports.$set('binding', binding.generate());