I was able to repro this on the mac canary, but only on first startup.

With a few minutes of investigation, it looks like the call to the passwords private api returns an empty list the first time it's called.

fwiw: it seems like there's a few solutions to this:

It looks like calling RespondLater() instead of RespondNow() from both GetSavedPasswordList and GetPasswordExceptionList in the API and using state in the delegate (i.e. is_initialized_ or simply set_password_{exception,}list_called_).

we may also be able to re-use the observers (and remove the getters if we can count on always getting an observation when registering).

also, see how the remove functions block on being initialized:
https://cs.chromium.org/chromium/src/chrome/browser/extensions/api/passwords_private/passwords_private_delegate_impl.cc?sq=package:chromium&dr=CSs&rcl=1477408745&l=71

i've looked into this a little bit, so i'll take it

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/80312194b99b0f8b03d0e5c9a3920b81399d6fd6

commit 80312194b99b0f8b03d0e5c9a3920b81399d6fd6
Author: dbeam <dbeam@chromium.org>
Date: Tue Nov 01 23:16:23 2016

MD Settings: fix chrome.passwordsPrivate empty list bug

R=rdevlin.cronin@chromium.org
BUG= 657215 

Review-Url: https://codereview.chromium.org/2468763002
Cr-Commit-Position: refs/heads/master@{#429148}

[modify] https://crrev.com/80312194b99b0f8b03d0e5c9a3920b81399d6fd6/chrome/browser/extensions/api/passwords_private/passwords_private_api.cc
[modify] https://crrev.com/80312194b99b0f8b03d0e5c9a3920b81399d6fd6/chrome/browser/extensions/api/passwords_private/passwords_private_api.h
[modify] https://crrev.com/80312194b99b0f8b03d0e5c9a3920b81399d6fd6/chrome/browser/extensions/api/passwords_private/passwords_private_apitest.cc
[modify] https://crrev.com/80312194b99b0f8b03d0e5c9a3920b81399d6fd6/chrome/browser/extensions/api/passwords_private/passwords_private_delegate.h
[modify] https://crrev.com/80312194b99b0f8b03d0e5c9a3920b81399d6fd6/chrome/browser/extensions/api/passwords_private/passwords_private_delegate_impl.cc
[modify] https://crrev.com/80312194b99b0f8b03d0e5c9a3920b81399d6fd6/chrome/browser/extensions/api/passwords_private/passwords_private_delegate_impl.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/83bb086878243e77279db7ae9d973649a0453f45

commit 83bb086878243e77279db7ae9d973649a0453f45
Author: dbeam <dbeam@chromium.org>
Date: Wed Nov 02 02:08:12 2016

MD Settings: test passwordsPrivate.get{SavedPassword,PasswordExceptions}List

Also, separate list initialization (blocks on less things).

R=rdevlin.cronin@chromium.org
BUG= 657215 

Review-Url: https://codereview.chromium.org/2466273004
Cr-Commit-Position: refs/heads/master@{#429183}

[modify] https://crrev.com/83bb086878243e77279db7ae9d973649a0453f45/chrome/browser/extensions/api/passwords_private/passwords_private_delegate_impl.cc
[add] https://crrev.com/83bb086878243e77279db7ae9d973649a0453f45/chrome/browser/extensions/api/passwords_private/passwords_private_delegate_impl_unittest.cc
[modify] https://crrev.com/83bb086878243e77279db7ae9d973649a0453f45/chrome/test/BUILD.gn