In short: Chrome OS devices built in a convertible or tablet configuration may soon be able to hide the top UI in-browser upon scrolling as early as Chrome 70 or version 71, judging by a recently spotted commit in the Chromium Gerrit. The feature, dubbed 'top-chrome slide' in the flags menu, has now been turned on by default in the Canary Channel. As a result, those who are on the developer-driven beta channel of the OS can now scroll down in Google Chrome on a Chrome OS device in tablet mode and the browser's UI will hide automatically.
Background: For clarity, this feature was actually reported in earlier versions of the OS but was turned off by default, likely due to some bugs with its use. After the latest update to the Canary Channel, none of the flags in the hidden settings menu for the browser will need to be adjusted. Instead, the change makes hiding the UI as part of page scrolling the defacto standard behavior the browser's UI for those on the developer version. As expected, the new UI works exactly as it does in Android and seems to be just another step in the long list of changes brought to bring the two OS more closely together in functionality and appearance. That means that scrolling a page down will slide the menu, URL Omnibox, and all open tabs up and out of sight, freeing up more of a given display to show a website's contents. Meanwhile, scrolling back toward the top of the page will cause the UI to slide back down into view.
With that said, users on Android don't need to scroll back up to the very top of a page before the UI reappears. That allows tab switching and menu access without the user having to navigate the way up and subsequently losing their position on the page when they switch back. For Chrome OS, the feature doesn't seem to have progressed that far yet and still seems to require users are at the top of the page before the UI reappears. So that's at least one kink in the system that will need to be worked out before the change arrives for the average user in the consumer-ready Stable Channel.
Impact: The fact that top-chrome slide is now turned on by default essentially shows that it is progressing through the test process fairly quickly. That's not surprising since it has been in place for Android users for quite some time already. With Chrome OS, the difference that makes will almost certainly be more pronounced, however, since it will free up a more visibly perceptible number of pixels for content instead of using those for the browser itself.