I wonder if export should be disabled while the list in settings is loading. That's what Android does (it also uses PasswordManagerPresenter::GetAllPasswords), see SavePasswordsPreferences#onPrepareOptionsMenu.

Finally, looking at ios/chrome/browser/ui/settings/save_passwords_collection_view_controller.mm, there also seems to be a time interval when the settings page is still waiting for onGetPasswordStoreResults to be called. ioanap@ -- is the export button available during that time interval?

Just looked at it again and yes, the export button is disabled until the list of saved passwords is populated. 

For reference: this happens in SavePasswordsCollectionViewController via loadModel => updateExportpasswordsItem which is called once when the controller is initialized (list is empty, so the button is set to disabled) and then once when the passwords are ready (via reloadData).

I think the UX is the wrong level to solve the fact a method may return incorrect data. We're only hiding the bug and hoping we don't step on it again in the future. I would only consider it as temporary hack to make it to M66.

Why not put there a DCHECK then?
Making it block seems like adding unnecessary complexity, when the design could be kept so that this is not even called before the passwords are available.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d57ac0affdfc1080acc0de78384260798681b92c

commit d57ac0affdfc1080acc0de78384260798681b92c
Author: Christos Froussios <cfroussios@chromium.org>
Date: Tue Feb 06 18:32:11 2018

[Password Manager] Show export menu item only for a non-empty password list

Exporting an empty password list has no value for the user. Additionally,
exporting while the password list is still loading is undefined behaviour.

For these reasons, we only show the Export Passwords menu item only once
the password list has been read and is non-empty.

Bug:  789561 , 805534 , 807975 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Ief82b4b46a231402dbaa7251e514c4078f7be31a
Reviewed-on: https://chromium-review.googlesource.com/897486
Commit-Queue: Christos Froussios <cfroussios@chromium.org>
Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534728}
[modify] https://crrev.com/d57ac0affdfc1080acc0de78384260798681b92c/chrome/browser/resources/settings/passwords_and_forms_page/passwords_section.js

The implementation works around this. There is no motivation to change the implementation itself.