Record time to navigation/tab-closed after HTTP-bad warning

This CL adds UMA metrics to record the time after displaying a
password/credit-card field on an HTTP page until the user navigates or
closes the tab.

By comparing these metrics for users who see the omnibox warning and
those who only get a console warning, we hope to get some idea of how
the HTTP-bad omnibox warning affects user behavior.

BUG=663924

Review-Url: https://codereview.chromium.org/2499243002
Cr-Commit-Position: refs/heads/master@{#433411}
(cherry picked from commit 5c563b099036a96fc1e2b0ede70ec83d14012bc6)

Review URL: https://codereview.chromium.org/2520923003 .

Cr-Commit-Position: refs/branch-heads/2924@{#30}
Cr-Branched-From: 3a87aecc31cd1ffe751dd72c04e5a96a1fc8108a-refs/heads/master@{#433059}
4 files changed