Add button to add new FSP services to Files app.

ui/file_manager/file_manager/foreground/js/file_manager.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.
 
 /**
  * FileManager constructor.
  *
  * FileManager objects encapsulate the functionality of the file selector
  * dialogs, as well as the full screen file manager application (though the
  * latter is not yet implemented).
@@ skipping 928 matching lines @@
     var directoryTree = /** @type {DirectoryTree} */
         (this.dialogDom_.querySelector('#directory-tree'));
     var fakeEntriesVisible =
         this.dialogType !== DialogType.SELECT_SAVEAS_FILE;
     DirectoryTree.decorate(directoryTree,
                            assert(this.directoryModel_),
                            assert(this.volumeManager_),
                            assert(this.metadataModel_),
                            fakeEntriesVisible);
     directoryTree.dataModel = new NavigationListModel(
-        this.volumeManager_, this.folderShortcutsModel_);
+        this.volumeManager_,
+        this.folderShortcutsModel_,
+        new NavigationModelCommandItem(
+          util.queryDecoratedElement('#add-new-services', cr.ui.Command)));
 
     this.ui_.initDirectoryTree(directoryTree);
   };
 
   /**
    * Sets up the current directory during initialization.
    * @private
    */
   FileManager.prototype.setupCurrentDirectory_ = function() {
     var tracker = this.directoryModel_.createDirectoryChangeTracker();
@@ skipping 335 matching lines @@
       out += this.initializeQueue_.pendingTasks[key].toString() + '\n';
     }.bind(this));
 
     out += '2. VolumeManagerWrapper\n' +
         this.volumeManager_.toString() + '\n';
 
     out += 'End of debug information.';
     console.log(out);
   };
 })();