Chrome 73 is going to include support for macOS 10.14's dark mode, with an alternative color scheme for its user interface that cuts the brightness. It's now clear that a Windows version of the same is in development, though it seems to trail the macOS version.
A bug report was spotted by Techdows, and preliminary work has been started to bring Windows its dark mode. Unlike its macOS counterpart, which should track the operating-system mode, the Windows dark mode currently has to be forcibly turned on with a command-line switch. Adding "--force-dark-mode" to the command line of current builds of Chrome 73 makes everything dark.
The macOS work has top priority (P1). The Windows work is only P2 (originally P3), surprisingly suggesting that it's less important, enough though Chrome has far more Windows 10 users than it does macOS users. Development of the Windows theme was at least, for a time, hindered by one of the developers not having a Windows laptop to use.