Sky was previously Razer. Cobalt is a YouTube project they use for TVs and such.

The first time I heard of Flutter was as Sky in 2015. I can't find any article or video about Razer. Please provide a source.

Source: I worked next to the team.

Cobalt appears to be exactly what you're looking for. How was Razer different?

Razer was by the Chrome team, subsetting (plus some web-compat polyfillable superset) HTML and CSS consciously by design for performance and code size. It would have been great for Cobalt's target.

Cobalt is mostly whatever YouTube can afford to implement and run on TVs.