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 75e146b27ac3aecb0edec6f34d51019a0d61a3f7..54cf35f6743e09bc7700242bdd03fda795f4adff 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