Chrome Version: 64.0.3260.0 (Official Build) canary (64-bit)
OS: OSX 10.12.6

What steps will reproduce the problem?
(1) Navigate to data:text/html, <textarea>
(2) Typing some misspelled words
(3) Press ⌘+:

What is the expected result?

The spelling panel appear, showing the next misspelled word

What happens instead?

The spelling panel doesn't appear

Btw, ⌘+; works fine.