GitLab

This changes the app banner content setting from being a dictionary of
app key to bool, to being a dictionary of app key to dictionary.

The sub dictionary contains one bool for whether the banner has been
blocked, and also a list of dates. The list of dates will contain at
most 14 dates, and will be used to record distinct dates on which the
banner could have been shown.

This is to allow more complex triggering. The goal is to actually show
banners if they could otherwise have been shown on a previous date in
the last 14 days.

Note the complex triggering is not currently used.

BUG=452825

Review URL: https://codereview.chromium.org/884373002

Cr-Commit-Position: refs/heads/master@{#314266}