Chrome Version       : 65.0.3325.56

In extensions/browser/api/networking_private/BUILD.gn there is a line that says:
  not_needed(default_sources)

The argument to not_needed should be a list of the names of variables that are not needed, so this is not correct usage.  Inside gn we end up hitting the NOTREACHED() line in Scope::MarkUsed as the and in some builds this ends up terminating gn.

To reproduce this issue:
(1) $ tools/gn/bootstrap/bootstrap.py --debug --no-rebuild --output=out/gn
(2) $ out/gn/gn gen out/default

I find that gn aborts at the location described above.

It feels a bit like there are two issues here, the first is that the BUILD.gn file is wrong and the second is that gn doesn't detect this and display a useful error message.