Make Service Worker registration work properly (don't use outdated steps)

[mgiuca]

This change (choose one):

• Breaks existing normative behavior (please add label "breaking")
• Adds new normative requirements
• Adds new normative recommendations or optional items
• Makes only editorial changes (only changes informative sections, or
  changes normative sections without changing behavior)
• Is a "chore" (metadata, formatting, fixing warnings, etc).

Commit message:

Make Service Worker registration work properly (don't use outdated steps).

Closes #789.

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Preview | Diff

[kenchris]

Does this PR have unrelated changes? It seems so

[mgiuca]

Ugh, yes, this is because GitHub doesn't respect upstream branches in Git. This PR is dependent on #790 which hasn't landed yet, and I don't think there's any way for GitHub to show just the relevant changes.

Please look at this delta.

[mgiuca]

@marcoscaceres While I'm on a roll with Manifest...

Edit: Please look at this delta.

1. I need a bit of help with ReSpec. (General ReSpec comments appreciated; I've been trying out the new (?) |var|.{{Method}} syntax.) I tried to add a reference to RegistrationOptions.type using "for="RegistrationOptions"" (the "for" clause working well for all the other methods and members). But I get a conflict with the other definition of ECMAScript's Type() function. I thought "for" was supposed to disambiguate it by saying "this type is for RegistrationOptions only" but it still conflicts.
2. This is a bit nasty but it's in the current text too: (the old text reads: "the state of the settled promise determines whether the installation succeeded or not") --- the fact that if service worker registration fails, the whole installation is aborted, even though service worker registration is optional. So some user agents will not bother to register a (failing) SW, thus successfully installing, and others will try to register the SW and fail the install. Is that "okay" (essentially making a best effort to check, but you don't have to check). Or should we succeed the install even if SW registration fails, for consistency across user agents?

[mgiuca]

The upstream PR has now merged, so this PR's delta is correct.

[marcoscaceres]

Approved with caveat the the service worker stuff will be deleted right after (as decided in #800).

[kenchris]

Well Jeffrey (talked at TPAC) says to please not do that as he is going to use that innWeb Packaging which uses web app manifest

[kenchris]

@jyasskin could you comment?

[marcoscaceres]

Sure, but the multi-implementer problem remains. Not sure at this point we want to support this in Gecko, but need to check if WebKit supports it.

[jyasskin]

We might use the serviceworker field to have navigation to a web package automatically install its service worker before the start page loads, but I think we can re-add the field if/when we do that. It won't hurt us to remove it until then.

[marcoscaceres]

Ok, let's proceed with the plan to remove it... we can always bring it back.

[mgiuca]

Oops, thanks for closing this out.