Add UKM metrics for password submission indicator.

The CL is created in response to https://chromium-review.googlesource.com/c/chromium/src/+/1057235
SubmissionIndicatorEvent is already recorded via UMA. It indicates the event that made the password manager believe that there was a submission. The UKM is to be recorded only when a password is saved. It means that the submission detectioln was probably correct.

Bug: 842643
Change-Id: Ic381ee93de7459d7d942a9ee1b27d43e39095fc7
Reviewed-on: https://chromium-review.googlesource.com/1060034
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Reviewed-by: Dominic Battré <battre@chromium.org>
Commit-Queue: Vasilii Sukhanov <vasilii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#559236}
4 files changed