Chrome Version: 64.*
OS: Win, ???

What steps will reproduce the problem?
(1) Launch Chrome
(2) Launch Chrome again from command line, include --user-data-dir flag
    to ensure full rendezvous execution.

What is the expected result?

Rendezvous process shouldn't touch anything in the user-data-dir because it's actively being used by the main Chrome process.

What happens instead?

Rendezvous process exits cleanly.  Since this removes the active BrowserMetrics file it has been working with, the ChromeMetricsServiceClient object has been properly destroyed.  Presumably, the metrics were collected before deleting the file and that collection was written as a persistent log to the user-data-dir.

I'm not sure how to verify my claim that the log is written to the user-data-dir; I have observed only that the metrics file is deleted and, given that only happens in one place, surmised the rest.

From a metrics point-of-view, it would be okay for the process to hard-exit after signalling the main Chrome process.  The metrics file would then be collected and read by that main process.