sessions: add debugging code to help identify loss of data

Some ChromeOS logs indicate that SessionService is getting created
multiple times. That the SessionService is created multiple times
isn't itself a problem, what is a problem is if it's recreated at a
time we don't expect (perhaps shutdown), so that the session data ends
up getting clobbered. This adds logging and crash-without-dump to
help track down what is happening.

This also moves logging of the start event to SessionService. This is
done as StartupBrowserCreator isn't always created in some situations
(namely chromeos startup).

BUG=1245816
TEST=none

Change-Id: I6331c6ca0b67982f5796420ba303b7031351aaca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3139174


Commit-Queue: Scott Violet <sky@chromium.org>
Reviewed-by: David Bienvenu <davidbienvenu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#917739}