Chrome Version: 61.0.3163.100 (Official Build) (64-bit)
OS: OSX 10.12.6, goobuntu trusty 14.04

What steps will reproduce the problem?
(1) In chromium gerrit https://chromium-review.googlesource.com/c/chromium/src/+/741001
(2) Press "Reply" button at the top of the page or below individual messages
(3) Compose a reply and hit "Send" button.

What is the expected result?
Reply sends.

What happens instead?
Alert in the corner reads "Server error: internal server error", reply becomes editable again.