the login_manager (session_manager) supports two filesystem knobs:
- /mnt/stateful_partition/etc/enable_chromium_coredumps
  - creates /var/coredumps (as chronos?)
  - sets setrlimit(RLIMIT_CORE) to RLIM_INFINITY
  - sets /proc/sys/kernel/core_pattern to /var/coredumps/core.%e.%p
- /mnt/stateful_partition/etc/enable_chromium_minidumps
  - exports CHROME_HEADLESS=1
  - creates /var/minidumps (as chronos?)
  - symlinks .config/google-chrome/Crash Reports to /var/minidumps

crash-reporter itself has knobs which largely covert this:
- /root/.leave_core
  - created on all dev & test images
  - tells crash-reporter to not delete coredumps after creating minidumps/crash reports
- /mnt/stateful_partition/etc/collect_chrome_crashes
  - created by autotests
  - tells crash-reporter to collect crash reports even for Chrome (normally ignored)

common Chrome docs already talk about setting CHROME_HEADLESS=1, so people, if they really need it (do they?) can do so in /etc/chrome_dev.conf.

so i think the existing crash-reporter functionality covers everything session_manager has.  it's not like the session_manager knobs are OS-independent, they're entirely CrOS-specific.  pointing people to crash-reporter docs for all things CrOS/crash related makes the most sense to me.