Safari doesn't let us get at the entire collection of passwords in the keyring unless the user provides permission...for...each...password, which is a pretty garbage import experience.

Our current solution is actually to have the user import the CSV file that Safari can export in about:logins.

What we'd like to do is expose Passwords as a resource that is importable from Safari, but if the user chooses it, to navigate the user to the SAFARI_PASSWORD_PERMISSION page that was added in bug 1818789, and prompt the user to browse to the CSV file that Safari exports.

Then we can import the other Safari resources that we do have access to and the passwords all in one shot.

This depends on bug 1821187 because we're probably going to want to re-use the file migration mechanism for the special Safari case here.

Note that the data review for the browser.migration.safari_password_file telemetry event is covered by the data-review in bug 1824786.

Safari doesn't let us import all passwords from Keychain at once. Instead,
the user needs to authorize each read from Keychain one by one. This is
not tenable for password import.

Instead, we show the user instructions on how they can export their passwords
from Safari into a CSV file that can then be imported. This patch adds support
for showing those instructions (which had landed earlier in bug 1818789) and
then importing from that CSV file upon selection.

The data-review for the safari_password_file Telemetry event being used here
was done earlier in bug 1824786.

Backed out for causing failures at browser_disabled_migrator.js.

Backout link: Backed out for causing failures at browser_disabled_migrator.js.

Push with failures: https://treeherder.mozilla.org/jobs?repo=autoland&resultStatus=testfailed%2Cbusted%2Cexception%2Cretry%2Cusercancel&revision=863fae78db03c2bffe5d860a7ada23a66d3634ad

Failure log:
https://treeherder.mozilla.org/logviewer?job_id=417403196&repo=autoland&lineNumber=6262
https://treeherder.mozilla.org/logviewer?job_id=417403463&repo=autoland&lineNumber=5299
https://treeherder.mozilla.org/logviewer?job_id=417403028&repo=autoland&lineNumber=20206

This also started to permafail: https://treeherder.mozilla.org/jobs?repo=autoland&group_state=expanded&resultStatus=success%2Ctestfailed%2Cbusted%2Cexception%2Cretry%2Cusercancel&revision=863fae78db03c2bffe5d860a7ada23a66d3634ad&test_paths=browser%2Fcomponents%2Fnewtab%2Ftest%2Fbrowser&selectedTaskRun=IJgx35QzQWmQz9u62TTkKw.0

Failure log: https://treeherder.mozilla.org/logviewer?job_id=417403098&repo=autoland

https://hg.mozilla.org/mozilla-central/rev/eb8042169586