Enable importing passwords from Firefox

[evq]

Auditors: @darkdh

requires brave/muon#216
closes #9292

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.

Test Plan:

Reviewer Checklist:

Tests

• Adequate test coverage exists to prevent regressions
• Tests should be independent and work correctly when run individually or as a suite ref
• New files have MPL2 license header

[darkdh]

you will also need to remove
importer.on('add-password-form', (e, detail) => {})
since we have different implementation on muon brave/muon#216

[darkdh]

Please squash all commits into one, thanks.

[NejcZdovc]

Please add github auto-closing keyword into squashed commit

[bsclifton]

Holding off on merge until Muon code is accepted

Changes look great- nice work, @evq 😄

[cezaraugusto]

muon code was accepted, @evq could you pls rebase?

[cezaraugusto]

also pls remove label once you do, thanks!

[evq]

I rebased, waiting on a muon build to retest then I will push / remove the label

[evq]

@cezaraugusto I just pushed my rebased version, though I don't seem to be able to remove the label

[bridiver]

@evq does this have any moun dependencies?

[darkdh]

muon dep has already been merged
brave/muon#216

[bridiver]

this needs to wait for a 4.2.x build (and update b-l 0.19) before merging. Should be ready by tomorrow

[evq]

@bridiver is this good to merge since bd36f33 updated muon to 4.2.2?

[bridiver]

++

[hh-here]

I suspect that there's something I don't 'get'.
I'm running: Linux Mint 17.3 Rosa
&

Brave	0.19.6
rev	3be25d4
Preferences; Import Now; Saved Passwords => A box which tells me that it has done the biz' for both Chromium Version 59.0.3071.109
&
Firefox 54.0 (64-bit)
Then with Password Manager = Brave Built In
Security; Manage Passwords => No passwords have been saved

Q1. Are the passwords managed / saved elsewhere?
Q2. Is there something I have missed?

PS. The Firefox importing was a couple of seconds, the Chromium was 10s of seconds.