Fix potential flakiness in Files.app test

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

Index: ui/file_manager/file_manager/foreground/js/file_manager.js
diff --git a/ui/file_manager/file_manager/foreground/js/file_manager.js b/ui/file_manager/file_manager/foreground/js/file_manager.js
index 14fc3b7e103cb02a285fab1dc8f70279a7958408..432f3deb27b045aeba12f7b9c2e79b413fb82dcf 100644
--- a/ui/file_manager/file_manager/foreground/js/file_manager.js
+++ b/ui/file_manager/file_manager/foreground/js/file_manager.js
@@ -598,6 +598,9 @@ FileManager.prototype = /** @struct */ {
     this.initializeQueue_.add(
         this.initFileSystemUI_.bind(this),
         ['initAdditionalUI', 'initSettings'], 'initFileSystemUI');
+    this.initializeQueue_.add(
+        this.initUIFocus_.bind(this),
+        ['initAdditionalUI', 'initFileSystemUI'], 'initUIFocus');
 
     // Run again just in case if all pending closures have completed and the
     // queue has stopped and monitor the completion.
@@ -804,6 +807,17 @@ FileManager.prototype = /** @struct */ {
   };
 
   /**
+   * One-time initialization of focus. This should run at the last of UI
+   *  initialization.
+   *
+   * @private
+   */
+  FileManager.prototype.initUIFocus_ = function(callback) {
+    this.ui_.initUIFocus();
+    callback();
+  };
+
+  /**
    * One-time initialization of import history observer. Provides
    * the glue that updates the UI when history changes.
    *