GitLab

PermissionMessageProvider:
- add GetPermissionMessageStrings which calls either the old or the new system, based on a field trial
- rename GetWarningMessages/GetWarningMessagesDetails to *Legacy*
- replace GetPermissionMessages by GetLegacyPermissionMessageIDs -> remove the old PermissionMessages type from the interface

Callers have *not* been updated to use the new GetPermissionMessageStrings yet.

TBRing trivial change in ephemeral_app_launcher.cc
TBR=asargent@chromium.org

BUG=398257

Review URL: https://codereview.chromium.org/1006453002

Cr-Commit-Position: refs/heads/master@{#320702}