When Crashpad self-monitoring is enabled, crashes in crashpad_handler
will be written to the crash report database and uploaded according to
the user's preference. Self-monitoring dedicates an additional
crashpad_handler process to serve as the handler for the original
instance. Having a dedicated process is somewhat expensive, so
self-monitoring is not enabled at all times.

An existing mechanism, the "fallback crash handler," is already in place
on Windows. The fallback crash handler does not create any additional
processes until a crashpad_handler crash occurs. The fallback handler
remains effective in cases where Crashpad's own self-monitoring is
disabled. The fallback handler and Crashpad self-monitoring have
different attributes, so there are no plans to move Windows entirely
onto Crashpad self-monitoring.

For branded Chrome, the dev channel gets Crashpad self-monitoring in 25%
of browser starts, and the beta channel gets it in 10% of browser
starts....