`add_theme_support( 'responsive-embeds' );` was added in #10477. We should add it to the [docs](https://github.com/WordPress/gutenberg/blob/master/docs/extensibility/theme-support.md), see also https://github.com/WordPress/gutenberg/pull/10477#issuecomment-428854033
add_theme_support( 'responsive-embeds' );was added in #10477.We should add it to the docs, see also #10477 (comment)