Show a local folder's size in QuickView.

ui/file_manager/file_manager/foreground/elements/files_metadata_entry.js

 // Copyright 2016 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 FilesMetadataBox = Polymer({
   is: 'files-metadata-entry',
 
   properties: {
     key: {
       type: String,
       reflectToAttribtue: true,
     },
 
     // If |value| is empty, the entire entry will be hidden.
     value: {
       type: String,
       reflectToAttribtue: true,
     },
+
+    loading: {
+      type: Boolean,
+      reflectToAttribtue: true,
+      value: false,
+    },
   },
 
 });