Add new metrics for the password manager onboarding experience

This CL adds two new metrics to be recorded for the onboarding. Both of
them represent the result of the password saving flow, which can either be
one of the infobar dismissals or an earlier dismissal of the onboarding
dialog. The first metric is recorded for all saving prompts and the second
is only recorded if the onboarding was actually shown during the current flow.

Bug: 983445
Change-Id: I8af3d451fa0b365632cb0c980a10a48f5c1785ea
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1796342
Commit-Queue: Andrei Chulkov <achulkov@google.com>
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695654}
14 files changed