Reproduceable on all Chrome channels and version.
Install Chrome Canary on latest Mac OS 10.14 developer beta from developer.apple.com 
In system preferences, general, set Appearance to "Dark".
This will change all Mac OS menues and controls to use white on black which are high contrast and are much easier to read for visually impaired users such as myself.
Note that Apple Apps such as Mail also apply the White on black to all controls such as mail liast.

Chrome however still does not detect or support Dark mode.

I managed to force web pages to high contrast using the high contrast chrome plug-in which makes Gmail looks more like Apple mail in Dark Mode.
Hoeever the chrome bar and menu as well as the google.com homepage are still white.

Expected behaviour:
1. Chrome Flag to turn Dark mode on/off
2. Chrome should auto detect Dark mode in system preferences and either switch Chrome to Dark mode or offer the user to turn on Chrome Dark Mode.

Note that while this will be very important to visually impaired users, many sighted users use Dark mode, especially developers and the current Chrome bar is very painfull. 

Chrome should also support High contrast (Dark mode web pages) as a built in flag rather than (A somewhat unstable) extension.