From testing, appears to be a regression from:

https://chromium.googlesource.com/chromium/src/+/81b0a99860c6fe445637371a5322a468b237fb72

The problem is that there are 2 FileNetLogObserver classes being instantiated that write to the same file.

The first one is the one I expect:
   net_log::ChromeNetLog::StartWritingToFile().

However a bit later, there is also:
  content::NetworkServiceImpl::MojoNetLog::MojoNetLog().


Matt, what is the solution for this? One possibility is to change the command-line used by MojoNetLog so it doesn't trigger in this case. But I don't know much about the NetworkService and how it is expected to co-habitate and share command line flags with Chrome.

Oops!  I added the in-process bogus NetworkService just last week.  My suggestion is to make NetworkService ignore the command line command line flags when creating in-process (When created with NetworkService::Create).

This does seem ugly, but I'll need to be adding other magic for that path, too (Like making a NetworkChangeNotifier only when it's out of process.  Will need to come up with something prettier long term, though)

Is the difference in NetworkService construction that |registry| will be nullptr when doing inprocess/test construction and non-nullptr otherwise?

(Looking for where to make the decision to inspect netlog command line flags).

It's also nullptr in unit tests, and I suspect we want to construct the full object in unit tests, so I'd suggest a separate constructor for the ::Create path instead (Or add another constructor parameter).

Eventually, we'll want to always use the one the NetworkService creates, at which point we can get rid of the current ChromeNetLog, but I think that's a bit too much work to worry about now (Logging network changes and net-export are the two big things, off the top of my head, though sure there are others)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4eca3b25f42e96ab59dfc0e8c4811ae7d7fad404

commit 4eca3b25f42e96ab59dfc0e8c4811ae7d7fad404
Author: Eric Roman <eroman@chromium.org>
Date: Tue Jul 18 21:53:21 2017

Don't write to --log-net-log from MojoNetLog when running in-process.

Bug:  745877 
Change-Id: I05d3fcdbe55509d808f0ab696b159ca22876a0b8
Reviewed-on: https://chromium-review.googlesource.com/576358
Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Eric Roman <eroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487621}
[modify] https://crrev.com/4eca3b25f42e96ab59dfc0e8c4811ae7d7fad404/content/network/network_service_impl.cc

Apologies, applied the wrong component in bulk.