Make createAttribute() lowercase the input in HTML documents

[foolip]

Fixes #41

[foolip]

PTAL. I'm not sure if the argument name should be changed now that it isn't necessarily the verbatim localName, I just left it alone.

[annevk]

Oh I completely missed this. So Gecko now implements this simple behavior and Chrome does too?

[foolip]

No, it hasn't been implemented yet, but based on the use counters I added in Blink and the telemetry in Gecko, we seem to have agreed that this is the approach we should try. See https://bugzilla.mozilla.org/show_bug.cgi?id=1176313

[foolip]

If you want to wait with the spec change until it's been shipped, that's fine, it's just not the usual order.

[foolip]

@bzbarsky, are you now attempting to implement what the spec says plus the change in this PR in Gecko, or what is the whole "package" or changes being attempted at the same time?

[bzbarsky]

@foolip I've landed the change in this PR in Gecko nightlies. See https://bugzilla.mozilla.org/show_bug.cgi?id=1205364

I'm also attempting to reland the rest of the "follow the spec" changes; that's being tracked in https://bugzilla.mozilla.org/show_bug.cgi?id=1176313 and I expect to check it in sometime today.

[foolip]

That sounds great, @bzbarsky! If those changes make it successfully to Firefox stable, I'd like to attempt the same spec sync in Blink.