AMP: Stylesheet 'jetpack-widget-social-icons-styles' is enqueued even if Social Icons widget is never used

[westonruter]

The stylesheet for the Social Icons widget is enqueued unconditionally even when the widget not used on the page:

jetpack/modules/widgets/social-icons.php

Lines 50 to 55 in 429d964

	/**
	* Styles for front-end widget.
	*/
	public function enqueue_icon_scripts() {
	wp_enqueue_style( 'jetpack-widget-social-icons-styles', plugins_url( 'social-icons/social-icons.css', __FILE__ ), array(), '20170506' );
	}

Normally jetpack_implode_frontend_css would be true so this issue would not be noticed. However, when serving AMP pages, Jetpack opts-out of serving the concatenated CSS to facilitate the AMP plugin's CSS tree shaker to make it easier to stay below 50KB:

jetpack/3rd-party/class.jetpack-amp-support.php

Lines 32 to 33 in 429d964

	// disable imploding CSS
	add_filter( 'jetpack_implode_frontend_css', '__return_false' );

This then causes the CSS to be needlessly output on the frontend, as seen in the style[amp-custom] manifest comment:

253 B (40%): link#jetpack-widget-social-icons-styles-css[rel=stylesheet][id=jetpack-widget-social-icons-styles-css][href=https://weston.ruter.net/wp-content/plugins/jetpack/modules/widgets/social-icons/social-icons.css?ver=20170506][type=text/css][media=all]

There are 253 bytes, the .screen-reader-text rule, which survive the tree-shaking process. While this is very small, every byte counts when there is a 50KB limit.

And for sites that have other reasons to disable jetpack_implode_frontend_css, this needless enqueue slows down the performance of the frontend.