Stop worrying about tiny OOMs. Work towards #20449.
While going through these, I also changed the function signature in many
places where returning ThrowCompletionOr<T> is no longer necessary.
We got some errors while loading https://twinings.co.uk/ about this
interface missing, and it looked fairly simple so I sketched it out.
Note that I did leave some FIXMEs where it's not clear exactly which
metrics we should be returning.