[Autofill] Rename existing strike_database files

Renamed strike_database.h/cc to legacy_strike_database.h/cc and
strike_database_unittest.cc to legacy_strike_database_unittest.cc.
This is so that the files for the  new version of StrikeDatabase
can take the old name.

Bug: 884817
Change-Id: Id4d1496b792d93f7e38afdab1ddad0419ec27f10
Reviewed-on: https://chromium-review.googlesource.com/c/1330724
Reviewed-by: Fabio Tirelo <ftirelo@chromium.org>
Reviewed-by: Martin Šrámek <msramek@chromium.org>
Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Reviewed-by: Richard Coles <torne@chromium.org>
Reviewed-by: Jared Saul <jsaul@google.com>
Commit-Queue: Anne Lim <annelim@google.com>
Cr-Commit-Position: refs/heads/master@{#607707}
44 files changed