Blob URL store entries are not removed

[annevk]

Currently they are only removed if you invoke revokeObjectURL(). There's a statement of fact at https://w3c.github.io/FileAPI/#url

All URLs are revoked when the global that created the URL itself goes away.

but there are no corresponding requirements.

Credit: @yutakahirano

[mkruisselbrink]

Hmm? What about https://w3c.github.io/FileAPI/#lifeTime where we monkey patch the unloading document cleanup steps? (of course similar steps for workers are still missing).

[annevk]

Ah, great. Let's keep this for the remaining issues with that section then (also need to link remove).