This will create .aspx.designer.cs files in your project. But you may run into the following error next:
"The name 'objectName' does not exist in the current context"
If so check that you have the namespace declared around your class in the .aspx.designer.cs file, the Convert to Web Application action doesn't always add it:
public partial class Default
You may also need to update the Page Directive's Inherit attribute to include the namespace:
<%@ Page ... Inherits="Default" %>
<%@ Page ... Inherits="My.Namespace.Default" %>