Fix trivial type-check errors in file_manager.

ui/file_manager/file_manager/foreground/js/ui/scrollbar.js

Index: ui/file_manager/file_manager/foreground/js/ui/scrollbar.js
diff --git a/ui/file_manager/file_manager/foreground/js/ui/scrollbar.js b/ui/file_manager/file_manager/foreground/js/ui/scrollbar.js
index 5a8e42caafe39398357fbe17360815933a68d307..755fbecfc1a268420494a2ce0bcece6ed17c5ca0 100644
--- a/ui/file_manager/file_manager/foreground/js/ui/scrollbar.js
+++ b/ui/file_manager/file_manager/foreground/js/ui/scrollbar.js
@@ -13,7 +13,7 @@ var ScrollBar = cr.ui.define('div');
 
 /**
  * Mode of the scrollbar. As for now, only vertical scrollbars are supported.
- * @type {number}
+ * @enum {number}
  */
 ScrollBar.Mode = {
   VERTICAL: 0,
@@ -81,7 +81,9 @@ ScrollBar.prototype.attachToView = function(view) {
   this.view_.addEventListener('scroll', this.onScroll_.bind(this));
   this.view_.addEventListener('relayout', this.onRelayout_.bind(this));
   this.domObserver_ = new MutationObserver(this.onDomChanged_.bind(this));
-  this.domObserver_.observe(this.view_, {subtree: true, attributes: true});
+  this.domObserver_.observe(
+      this.view_,
+      /** @type {MutationObserverInit} */ ({subtree: true, attributes: true}));
   this.onRelayout_();
 };