Chrome is packed with plenty of useful features that make their way into the Android version of the application, but they don't always begin their journey in the stable version of the app. There are actually multiple versions of Chrome for Android, including a beta build and a dev channel build, both meant to be more experimental than the stable version that is widely used by the majority of the public. Right now, the stable version of Chrome is currently sitting at version 50, while the beta version of the app is at 51 where Google just removed the merge tabs option. The dev channel build is now at version 52, and Google has added in a new feature for users to try out if they like messing around with experimental features that may or may not make it to the stable build of the app.
These new additions pertain specifically to tabs in Chrome and are labeled as Herb. The new Herb feature has several variants of the way it can be applied, each having their own specific herb name, including Anise, Basil, Chive, Dill, and Elderberry. Each herb variant is meant to have its own way of handling the browser links and the app switcher. When choosing to use Anise or Basil as the herb variant, links will open up as a Chrome Custom Tab when tapped, although Basil will open up with an "X" as a replacement for the home button that you would usually see next to the address bar. This "X" would allow the user to tap it and return to the calling app that they were just using while the home button in the Anise variant fo the herb feature would obviously take you back to the configured home page.
Google is also experimenting with a new Chrome Custom Tab called the CCT V2, basically just version 2 of the Chrome Custom Tab, which users can experience if they set the herb variant to Elderberry. It will likely be a while before any of herb feature variants make their way to a stable build, at which point they may not even be referred to as herb. For now, if you're curious to test the feature out, you can do so by typing chrome://flags/#tab-management-experiment-type into the address bar once you open up the dev channel Chrome app.