Files app: Work around the issue about opening menus by keeping references to <hr>s.

ui/file_manager/file_manager/foreground/js/ui/file_manager_ui.js

Index: ui/file_manager/file_manager/foreground/js/ui/file_manager_ui.js
diff --git a/ui/file_manager/file_manager/foreground/js/ui/file_manager_ui.js b/ui/file_manager/file_manager/foreground/js/ui/file_manager_ui.js
index ce7f1cb8b25a7bbb7ab51cb13a5f31f72767701e..d4a013cb30cc154bae4ed9f623240d7bba6ec5d5 100644
--- a/ui/file_manager/file_manager/foreground/js/ui/file_manager_ui.js
+++ b/ui/file_manager/file_manager/foreground/js/ui/file_manager_ui.js
@@ -34,6 +34,16 @@ function FileManagerUI(providersModel, element, launchParam) {
   this.dialogType_ = launchParam.type;
 
   /**
+   * <hr> elements in cr.ui.Menu.
+   * This is a workaround for crbug.com/689255. This member variable is just for
+   * keeping explicit reference to decorated <hr>s to prevent GC from collecting
+   * <hr> wrappers, and not used anywhere.
+   * TODO(fukino): Remove this member variable once the root cause is fixed.
+   * @private {!Array<!Element>}
+   */
+  this.separators_ = [].slice.call(document.querySelectorAll('cr-menu > hr'));
+
+  /**
    * Error dialog.
    * @type {!ErrorDialog}
    * @const