The History with Gesture flag for Chrome is a flag that can be enabled on your mobile device at chrome://flags/#enable-gesture-navigation. This is for devices running the stable channel of Chrome. If you are using Chrome beta or Dev then the flag has a different name so you will need to go to chrome://flags/#overscroll-history-nagivation
With this flag enabled you will be able to swipe right or left to go back to a previous page or go forward again respectively. When you swipe you will see a small circle with an arrow pointing the way you are navigating.
To enable you just need to paste the URL above into the chrome browser on your mobile device. Then click on default and change to enabled. Once you have done this click on restart browser and the swipe navigation will be enabled.
This is a great little feature that has been expected for a while but it is good to see that is now ready to go.
I'll start posting more flags soon as they are a great way to get the best out of your Chrome browser