Passwords are no longer stored using native backend. Switch to importing
from LoginDatabase like on other platforms.

Chromium change:

commit 6811de35a39128fb354f238bce350f9a4a643e9d
Author: Mohamed Amir Yosef <mamir@chromium.org>
Date:   Thu Jul 25 22:26:26 2019 +0000

    [PasswordManager] Stop Using Native Backends on Linux systems

    Recent migrations moved all users who have been using the keying to the
    LoginDatabase. This CL forces all users to using LoginDatabase
    instead of native backends on Linux.

    TBR=pcc@chromium.org

    Change-Id: Ibac11e68d8f354ecf7f3c9828d95777ea5b3df60
    Bug: 950269, 950267