Move to admin.php?customize=on&theme=$stylesheet, rather than juggling both...

Move to admin.php?customize=on&theme=$stylesheet, rather than juggling both template and stylesheet values. see #19910.

Combine the setup_theme() and customize_previewing() methods. Remove the set_template() and set_stylesheet() methods. Add set_theme() method to WP_Customize to store the working WP_Theme object. We will use this for the stylesheet and template.

Use the WP_Theme display() method when preparing headers for display, not get() or the deprecate properties.



git-svn-id: https://core.svn.wordpress.org/trunk@20496 1a063a9b-81f0-0310-95a4-ce76da25c4cd