User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/17.0 Safari/605.1.15

Steps to reproduce:

Spec PR: https://github.com/whatwg/streams/pull/1271 (for ReadableStream, others should follow for WritableStream and TransformStream)
WPT PR: https://github.com/web-platform-tests/wpt/pull/39520

The Bugbug bot thinks this bug should belong to the 'Core::DOM: Streams' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.