🐛 Update preconnects in amp-youtube component

[westonruter]

I just analyzed the resources which are loaded in a YouTube embed and they include:

• fonts.gstatic.com (for the fonts used in the title)
• yt3.ggpht.com (for the channel logo)
• i.ytimg.com (for the poster image)
• www.youtube.com (for JS and CSS assets)
• www.gstatic.com (for more JS assets)

Notably, s.ytimg.com is not among the domains that resources are loaded from, although it is still being preconnected to:

amphtml/extensions/amp-youtube/0.1/amp-youtube.js

Lines 117 to 121 in dccbba6

	preconnect.url(ampdoc, this.getVideoIframeSrc_());
	// Host that YT uses to serve JS needed by player.
	preconnect.url(ampdoc, 'https://s.ytimg.com', opt_onLayout);
	// Load high resolution placeholder images for videos in prerender mode.
	preconnect.url(ampdoc, 'https://i.ytimg.com', opt_onLayout);

I suggest removing this preconnect and instead replace it with a preconnect to fonts.gstatic.com since it is used to render the title text which is the actual LCP element (since the poster background image is excluded based on the current LCP heuristics).

[erwinmombay]

thanks @westonruter

[erwinmombay]

re-running jobs so we can merge

[erwinmombay]

@westonruter do you mind rebasing and re-pushing, ill try and get the tests green but i can seem to retrigger the bundle size to get it to pass

[westonruter]

@erwinmombay done, although I've also updated it to just remove the preconnect for fonts.gstatic.com. I found that no assets from that domain are loaded at all when emulating a mobile device. Fonts are only loaded on desktop. Since most AMP pages are served to mobile, it's probably best to just omit the fonts preconnect.

[erwinmombay]

@westonruter merged