[AF] Added Autocomplete Retention Policy feature flag to chrome://flags.

The entry will be removed as part of the overall flag cleanup:
crbug.com/920214

Also fixed a typo in the feature flag name.

Bug: 920741
Change-Id: Icefacf04b521d2c5195449c57ce3d310631bd310
Reviewed-on: https://chromium-review.googlesource.com/c/1406933
Commit-Queue: Sebastien Lalancette <seblalancette@chromium.org>
Reviewed-by: Fabio Tirelo <ftirelo@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622179}
16 files changed