Theme_Upgrader::check_parent_theme_filter()

	public function check_parent_theme_filter( $install_result, $hook_extra, $child_result ) {
		// Check to see if we need to install a parent theme.
		$theme_info = $this->theme_info();

		if ( ! $theme_info->parent() ) {
			return $install_result;
		}

		$this->skin->feedback( 'parent_theme_search' );

		if ( ! $theme_info->parent()->errors() ) {
			$this->skin->feedback( 'parent_theme_currently_installed', $theme_info->parent()->display( 'Name' ), $theme_info->parent()->display( 'Version' ) );
			// We already have the theme, fall through.
			return $install_result;
		}

		// We don't have the parent theme, let's install it.
		$api = themes_api(
			'theme_information',
			array(
				'slug'   => $theme_info->get( 'Template' ),
				'fields' => array(
					'sections' => false,
					'tags'     => false,
				),
			)
		); // Save on a bit of bandwidth.

		if ( ! $api || is_gc_error( $api ) ) {
			$this->skin->feedback( 'parent_theme_not_found', $theme_info->get( 'Template' ) );
			// Don't show activate or preview actions after installation.
			add_filter( 'install_theme_complete_actions', array( $this, 'hide_activate_preview_actions' ) );
			return $install_result;
		}

		// Backup required data we're going to override:
		$child_api             = $this->skin->api;
		$child_success_message = $this->strings['process_success'];

		// Override them.
		$this->skin->api = $api;

		$this->strings['process_success_specific'] = $this->strings['parent_theme_install_success'];

		$this->skin->feedback( 'parent_theme_prepare_install', $api->name, $api->version );

		add_filter( 'install_theme_complete_actions', '__return_false', 999 ); // Don't show any actions after installing the theme.

		// Install the parent theme.
		$parent_result = $this->run(
			array(
				'package'           => $api->download_link,
				'destination'       => get_theme_root(),
				'clear_destination' => false, // Do not overwrite files.
				'clear_working'     => true,
			)
		);

		if ( is_gc_error( $parent_result ) ) {
			add_filter( 'install_theme_complete_actions', array( $this, 'hide_activate_preview_actions' ) );
		}

		// Start cleaning up after the parent's installation.
		remove_filter( 'install_theme_complete_actions', '__return_false', 999 );

		// Reset child's result and data.
		$this->result                     = $child_result;
		$this->skin->api                  = $child_api;
		$this->strings['process_success'] = $child_success_message;

		return $install_result;
	}