Chrome version: 63.0.3207.0 (Official Build) canary (64-bit)
OS: macOS 10.12.6

I took some samples. Basically: Browser process main thread stuck in a synchronous write to the memlog pipe. Profiling process exists [hence pipe is valid], but not doing anything.

My guess is that there's a race condition: somehow the "service" in the profiling process is destroyed, but the profiling process [utility process] is still alive. The browser process thus becomes stuck in a synchronous write. This is a non-deterministic failure that occurs at shutdown.