Many Android apps display web content within themselves – this keeps the user from bouncing back and forth between the app and the browser, for example, when tapping on a link in Gmail. One way to do this is to use the WebView component, but Google believes that Custom Tabs are the better solution and it has now made them even better with a couple of improvements.
The first is Partial Custom Tabs. Instead of filling the whole screen, the web content can now only cover half, which improves the multitasking experience since you can still use the app (e.g. continue reading the email). You could use something like split-screen mode to achieve the same effect, but that requires extra interaction. The app developer decides on the initial size of the partial tab, the user is still free to go full screen if they prefer.
Custom Tabs are a feature that is provided by the user’s web browser of choice. If that browser doesn’t support Partial Custom Tabs, a full screen tab will be used instead. Obviously, Chrome supports this feature but so do other browsers.
Though if you do choose Chrome, the custom tab will support Chrome’s usual features including autofill for text fields and password fields.