Show UI when a folder is empty.

ui/file_manager/file_manager/foreground/js/empty_folder_controller.js

Index: ui/file_manager/file_manager/foreground/js/empty_folder_controller.js
diff --git a/ui/file_manager/file_manager/foreground/js/empty_folder_controller.js b/ui/file_manager/file_manager/foreground/js/empty_folder_controller.js
new file mode 100644
index 0000000000000000000000000000000000000000..9adeaeb1d2b70056fc8ebdb83aeef2aa20b0593a
--- /dev/null
+++ b/ui/file_manager/file_manager/foreground/js/empty_folder_controller.js
@@ -0,0 +1,82 @@
+// Copyright 2015 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.
+
+/**
+ * Empty folder controller.
+ * @param {!EmptyFolder} emptyFolder Empty folder ui.
+ * @param {!DirectoryModel} directoryModel Directory model.
+ * @constructor
+ * @struct
+ */
+function EmptyFolderController(emptyFolder, directoryModel) {
+  /**
+   * @private {!EmptyFolder}
+   */
+  this.emptyFolder_ = emptyFolder;
+
+  /**
+   * @private {!DirectoryModel}
+   */
+  this.directoryModel_ = directoryModel;
+
+  /**
+   * @private {!FileListModel}
+   */
+  this.dataModel_ = assert(this.directoryModel_.getFileList());
+
+  /**
+   * @private {boolean}
+   */
+  this.isScanning_ = false;
+
+  this.directoryModel_.addEventListener(
+      'scan-started', this.onScanStarted_.bind(this));
+  this.directoryModel_.addEventListener(
+      'scan-failed', this.onScanFinished_.bind(this));
+  this.directoryModel_.addEventListener(
+      'scan-cancelled', this.onScanFinished_.bind(this));
+  this.directoryModel_.addEventListener(
+      'scan-completed', this.onScanFinished_.bind(this));
+  this.directoryModel_.addEventListener(
+      'rescan-completed', this.onScanFinished_.bind(this));
+
+  this.dataModel_.addEventListener('splice', this.onSplice_.bind(this));
+}
+
+/**
+ * Handles splice event.
+ * @private
+ */
+EmptyFolderController.prototype.onSplice_ = function() {
+  this.update_();
+};
+
+/**
+ * Handles scan start.
+ * @private
+ */
+EmptyFolderController.prototype.onScanStarted_ = function() {
+  this.isScanning_ = true;
+  this.update_();
+};
+
+/**
+ * Handles scan finish.
+ * @private
+ */
+EmptyFolderController.prototype.onScanFinished_ = function() {
+  this.isScanning_ = false;
+  this.update_();
+};
+
+/**
+ * Updates visibility of empty folder UI.
+ * @private
+ */
+EmptyFolderController.prototype.update_ = function() {
+  if (!this.isScanning_ && this.dataModel_.length === 0)
+    this.emptyFolder_.show();
+  else
+    this.emptyFolder_.hide();
+};