Repro video in this link:
https://pantheon.corp.google.com/storage/browser/chromiumos-test-logs/bugfiles/cr/889973/

I don't think this is urgent, so P2 and M-71. The restriction to only mount the same share once was put in place because early in the implementation the share path was the key to lookup the credential and we wanted to avoid a case where it was ambiguous (or we chose incorrectly) if someone mounted the same path but with 2 different credentials.

However now we don't have that problem so this restriction is somewhat arbitrary and actually prevents the valid case of potentially wanting to mount the same share with different credentials.

Besides some possibility of user confusion (though they did this themself), there's no reason we need to even try to prevent this any more. Plus there are 
 other things like using escape characters, DNS aliases (short vs fully qualfied) or shares having multiple IP's/interfaces that would make it unreliable to 100% prevent this.

In the case that DNS is used (vs mDNS or NetBIOS) the name resolution is transparent to us anyway so even trying to use the IP address as a more reliable indicator wouldn't be possible.

Also its possible that a user could mount 2 shares with different names, then DNS settings change so that they both now point to the same IP address, when we reboot/remount we wouldn't be able to do anything about that.

So I'd actually be inclined to remove the restriction all together. If the user wants to mount the same share twice, that's up to them and there's no technical reason we need to prevent it.

Let's remove the restriction altogether since we no longer map credentials to paths