Chrome has a concept of "crash keys" which are pieces of metadata sent to the crash server when the browser crashes. They are written as part of in-process crash dumping.

For mash we're using the system crash_reporter for crashes, so we're not in-process. We need a way to export a little bit of metadata. vapier suggested environment variables.

Notes to self:
* environment is in /proc/<pid>/environ
* Record variables with setenv(), which allocates and copies strings on each call.
* For efficiency we could preallocate string buffers, use putenv() to connect them to the env variables, then copy our data into the buffers.