In the meantime, here's a polyfill https://github.com/jakearchibald/async-waituntil-polyfill

From https://github.com/w3c/ServiceWorker/issues/771:
"FYI, @catalinb has implemented this in gecko. It will ship in FF53 around April 2017."

I'll get back here later to implement this in M58.

ping?

Reset NextAction.

(blink worker triage) Reset NextAction.

We've heard from a few partners that it would be nice to not have to include a polyfill for this => Bumping the priority to 2 (desirable).

Leon, is this something you can work on soon?
Thanks a lot in advance!

Leon is creating a patch already: https://crrev.com/2877543003 .

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/eaf348dc9864d8073fe01472a91c33f21e3ec4b6

commit eaf348dc9864d8073fe01472a91c33f21e3ec4b6
Author: leon.han <leon.han@intel.com>
Date: Thu May 25 11:43:38 2017

[ServiceWorker] Allow waitUntil to be called multiple times asynchronously

Spec:
https://w3c.github.io/ServiceWorker/#dom-extendableevent-waituntil

BUG= 621440 
TEST=blink_tests
external/wpt/service-workers/service-worker/extendable-event-async-waituntil.https.html

Review-Url: https://codereview.chromium.org/2877543003
Cr-Commit-Position: refs/heads/master@{#474630}

[delete] https://crrev.com/929808a8f063d31a01b883ab8c81c21b838ad61b/third_party/WebKit/LayoutTests/external/wpt/service-workers/service-worker/extendable-event-async-waituntil.https-expected.txt
[modify] https://crrev.com/eaf348dc9864d8073fe01472a91c33f21e3ec4b6/third_party/WebKit/LayoutTests/external/wpt/service-workers/service-worker/extendable-event-async-waituntil.https.html
[modify] https://crrev.com/eaf348dc9864d8073fe01472a91c33f21e3ec4b6/third_party/WebKit/LayoutTests/external/wpt/service-workers/service-worker/resources/extendable-event-async-waituntil.js
[modify] https://crrev.com/eaf348dc9864d8073fe01472a91c33f21e3ec4b6/third_party/WebKit/LayoutTests/http/tests/serviceworker/chromium/resources/sw-test-helpers.js
[modify] https://crrev.com/eaf348dc9864d8073fe01472a91c33f21e3ec4b6/third_party/WebKit/LayoutTests/http/tests/serviceworker/resources/windowclient-navigate-worker.js
[modify] https://crrev.com/eaf348dc9864d8073fe01472a91c33f21e3ec4b6/third_party/WebKit/Source/modules/serviceworkers/ExtendableEvent.cpp
[modify] https://crrev.com/eaf348dc9864d8073fe01472a91c33f21e3ec4b6/third_party/WebKit/Source/modules/serviceworkers/RespondWithObserver.cpp
[modify] https://crrev.com/eaf348dc9864d8073fe01472a91c33f21e3ec4b6/third_party/WebKit/Source/modules/serviceworkers/RespondWithObserver.h
[modify] https://crrev.com/eaf348dc9864d8073fe01472a91c33f21e3ec4b6/third_party/WebKit/Source/modules/serviceworkers/WaitUntilObserver.cpp
[modify] https://crrev.com/eaf348dc9864d8073fe01472a91c33f21e3ec4b6/third_party/WebKit/Source/modules/serviceworkers/WaitUntilObserver.h

The NextAction date has arrived: 2017-06-01

It's fixed by c#11.