Add a refresh button for providers which do not support watchers.

ui/file_manager/file_manager/foreground/js/file_manager_commands.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.
 
 /**
  * Sets 'hidden' property of a cr.ui.Command instance and dispatches
  * 'hiddenChange' event manually so that associated cr.ui.MenuItem can handle
  * the event.
  * TODO(fukino): Remove this workaround when crbug.com/481941 is fixed.
  *
@@ skipping 1406 matching lines @@
     canExecute: function(event, fileManager) {
       var volumeInfo = this.getCommandVolumeInfo_(event, fileManager);
       event.canExecute = volumeInfo && volumeInfo.configurable;
       event.command.setHidden(!event.canExecute);
     }
   };
 
   return new ConfigureCommand();
 })();
 
+/**
+ * Refreshes the currently selected directory.
+ */
+CommandHandler.COMMANDS_['refresh'] = /** @type {Command} */ ({
+  /**
+   * @param {!Event} event Command event.
+   * @param {!FileManager} fileManager FileManager to use.
+   */
+  execute: function(event, fileManager) {
+    // TODO(mtomasz): Implement refreshing.
+  },
+  canExecute: function(event, fileManager) {
+    var currentDirEntry = fileManager.directoryModel.getCurrentDirEntry();
+    var volumeInfo = fileManager.volumeManager.getVolumeInfo(currentDirEntry);
+    event.canExecute = !volumeInfo.watchable;

[fukino, 2015/07/01 10:39:33]

Could you add null check as volumeInfo can be null?

[mtomasz, 2015/07/02 08:52:40]

Done.

+    event.command.setHidden(!event.canExecute ||
+        fileManager.directoryModel.getFileListSelection().getCheckSelectMode());
+  }
+});