Google introduced android Lollipop with lot of changes in its UI, many of them successful and continue in marshmallow and Android N,but Chrome merged tabs was not one of those features. After first making the old style tab management the default again several weeks back, the latest Chrome Dev build removes the merged tabs option entirely.
Merged tabs was an interesting idea in theory. Rather than having a tab switcher in the browser, you would just find your tabs in the main recent apps screen. The problem with merged tabs that you could easily lose tabs in there, and switching between Chrome tabs and other apps got Boring and time consuming. Most of people turned this feature off. Now you won't even be able to turn it on soon.
You will never find in upcoming Chrome Updates or may be with Android N updates, the new version of Chrome Dev (v51) on APK Mirror. The merged tabs option is just gone from the settings (see above, old on the left and new on the right). Since this is the dev channel, the change will likely move into beta and stable builds in the coming weeks. It's probably for the best.
Merged tabs was an interesting idea in theory. Rather than having a tab switcher in the browser, you would just find your tabs in the main recent apps screen. The problem with merged tabs that you could easily lose tabs in there, and switching between Chrome tabs and other apps got Boring and time consuming. Most of people turned this feature off. Now you won't even be able to turn it on soon.
You will never find in upcoming Chrome Updates or may be with Android N updates, the new version of Chrome Dev (v51) on APK Mirror. The merged tabs option is just gone from the settings (see above, old on the left and new on the right). Since this is the dev channel, the change will likely move into beta and stable builds in the coming weeks. It's probably for the best.
Source :- Android Police