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As pointed out by rhalavati@, the kWaitingForBrowserWindow ref was
removed when _any_ ScopedProfileKeepAlive was added. This does not match
intended use. This CL only removes kWaitingForBrowserWindow when a
kBrowserWindow ref is added.

Also, record histograms in ~ProfileManager(), to detect leaked
keepalives.

Bug: 88586
Change-Id: Iaec7d54109b7268059c8475261fef56ca1594c9f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2611050Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Commit-Queue: Nicolas Ouellet-Payeur <nicolaso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841491}