As phones get bigger and bigger, putting all the controls at the top of the display—Desktop OS style—becomes less and less ergonomic. Phones like the Galaxy S8 Plus have displays that are about six inches tall, so there is no way most people can reach the top of the display one-handed. It's with this in mind that Google is totally rethinking the Chrome mobile design with a new layout that puts all the controls—even the address bar—at the bottom of the screen.
For the past few months, Google has been experimenting with several new layouts, but these have all lived behind special settings flags. The above design just rolled out, by default, to the Chrome "Dev" channel on Android. We expect it to be headed to the Beta and Stable versions once all the bugs get worked out, and it should eventually see a release on iOS.