The new Google UI is now the default for all users, or it will be in a few hours. The black navbar is gone, and has been replaced with a new app launcher. The new UI is used across Google sites, in search, Gmail, Drive, and so on. Google even tested a version of the app launcher for YouTube, but it hasn't been made the default yet.
The move saves up a bit of space by removing the top navbar, but it makes accessing other Google products harder. Everything takes at least two clicks now and that's if you know you'll find the other Google products behind the app launcher next to your name.
Chrome users are also getting a revamped new tab page out of the deal with the Google Search homepage built in, as well as access to their most used sites. However, Chrome apps are now moved off to a new launcher, though not on all platforms.
The new Chrome new tab page is linked to the new Google navbar, but the two changes don't require each other, you can get one and not the other. With Chrome 30 now in the stable channel, the new tab page is the default for everyone on Windows, Chrome OS, and Mac.