[Files Ranking] Add a chrome flag.

Bug: 959679
Test: unit_tests
Change-Id: I9d7c7ae889ae460cb01c280ef79be751a4563889
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1765033
Commit-Queue: Tony Yeoman <tby@chromium.org>
Reviewed-by: Jia Meng <jiameng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#689781}
5 files changed