Partition Blob storage

[goodov]

Currently blob are accessible via URLs generated from URL.createObjectURL in a third-party context. We should partition the storage in a way that blobs can't be accessed in 3p context via URL generated in 1p context.

See also https://privacytests.org/ for blob storage partitioning test.

[goodov]

@pes10k if we can create some test page for this, it would be awesome :)

[pes10k]

Sure thing! For you @goodov , i have this: https://dev-pages.brave.software/storage/partitioning.html

[LaurenWags]

@goodov looks like https://privacytests.org/ has 1.37.x listed on main page and https://privacytests.org/nightly.html has 1.40.x on the Nightly page. Since neither of these will allow me to check 1.39.x, I'll use the page from #21746 (comment) for testing.

Any issues with this? Adding QA/Blocked until we confirm 👍🏻