Chrome Version: any recent stable release

What steps will reproduce the problem?
(1) run a CroSH command such as "network_diag --hosts".
(2) copy the resultant log file saved by CroSH to a USB drive
(3) plug said drive into a Windows machine.
(4) Windows behaves oddly with the log file because it doesn't like having : in a filename.

Windows reserves colon : character in filenames since it uses the colon to separate drive letter from file path since the early days of DOS:

https://www.quora.com/Why-are-colons-not-allowed-in-the-filenames-of-Windows-files

Log files generally look like:

network_diagnostics_2018-05-17.23:13:41.txt

we should just use something more universally compatible like - in place of the colons.

We often have customers running these diagnostics in guest mode or on a locked down device. They need to copy then email the files via a Windows machine and the colon trips them up.