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Adds Profile.Guest.Ephemeral.Lifetime and Profile.Guest.OTR.Lifetime
metrics to separately measure the life time of ephemeral and off the
record Guest profiles.

Bug: 1125474
Change-Id: I30b576b330367629198f800a5fea1248a7c65810
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2574848Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Reviewed-by: Caitlin Fischer <caitlinfischer@google.com>
Commit-Queue: Ramin Halavati <rhalavati@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834697}