Add bytes() method for reading bytes into a Uint8Array

[bakkot]

Edit: Replaced by #370.

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The Fetch API is getting a Uint8Array-returning bytes() method alongside its existing arrayBuffer() method, following the principle that APIs should generally vend byte buffers as Uint8Arrays.

This PR makes the same change for PushMessageData, which has its own distinct arrayBuffer method.

I'm assuming this is uncontroversial given the support from the three major implementations for doing this on Body, but I can open an issue and solicit explicit support separately if you'd prefer. I'll write tests if I get a signal that this is able to go forward.

It's unfortunate that getKey and applicationServerKey vend ArrayBuffers instead of Uint8Arrays, but it's too late to fix those now.

• Modified Web platform tests (link to pull request)

Implementation commitment:

• Chromium (https://bugs.chromium.org/p/chromium/issues/detail?id=)
• Gecko (https://bugzilla.mozilla.org/show_bug.cgi?id=)
• WebKit (https://bugs.webkit.org/show_bug.cgi?id=274119)

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Preview | Diff

[bakkot]

I couldn't find any existing tests to extend here, presumably due to #365. So I haven't written any tests for this. Happy to do so if there's a way to do it.

[martinthomson]

This looks fine. IPR commitments, less so. The IPR bot points to the necessary instructions.

[marcoscaceres]

Pinging @martinthomson and @beverloo for input and additional implementer support.

This is implemented in WebKit (thanks @annevk)

@bakkot, argh... small blocker on IPR, as this is substantive contribution. I'll need you to "make a non-member patent licensing commitment" unless you somehow join the working group. I'll see how we make that as painless as possible (hi @siusin, can you help us!).

[bakkot]

Signing such a commitment may be problematic since I do work for a web technologies company which is not a W3C member, even though this work was not done on their behalf. Given that this PR is basically trivial and involved no decisions, I'd prefer not to bother the lawyers just for this. I am happy to close it and let a member make an identical PR if it really can't be marked as non-substantive.

[marcoscaceres]

@bakkot, ok... sounds good.

Coincidently, I had the same idea! 😜
#370

[bakkot]

Sweet, thanks.

Closing in favor of #370.

[marcoscaceres]

Thanks for doing the actual work bakkot!