Record total time spent on a PiP window per AutoPiP reason

This CL adds a metric that represents the total time spent with an open
Picture in Picture window per AutoPiP reason (video conferencing or
media playback). Metric is recorded regardless of the Picture in
Picture window type (document vs video) and of the reason for closing
the window.

The metric will be helpful for determining if automatically opened
Picture in Picture windows are being closed shortly after opening,
signaling user dissatisfaction.

Bug: 368058093
Change-Id: I1bf0cd8576b2f5311c3f01c9fb72268c85ac05ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6203841
Commit-Queue: Benjamin Keen <bkeen@google.com>
Reviewed-by: Evan Liu <evliu@google.com>
Reviewed-by: Fr <beaufort.francois@gmail.com>
Cr-Commit-Position: refs/heads/main@{#1412528}