The flags and their defaults are part of the klog API and must not change.

The way it was implemented before, the current value of several flags was
written to the global config struct each time InitFlags was called. Not all
flags may get written concurrently, so this led to a data race when some other
goroutine was actively using klog. InitFlags also created new flag.Flag
instances for each call.

By creating flags once during init, InitFlags becomes entirely read-only and
thus safe to use concurrently.

What remains ambiguous is which flags may get changed at runtime. That was
underspecified before and doesn't get fixed here either, it just gets called
out as a potential problem.