An API called Bubbles has been introduced by Google. This new API would make it easier for app developers to push more visible notifications directly on top of the user’s display, just like Facebook Messenger’s Chat Heads feature.
People from XDA-Developers were able to manually enable the Android Message Bubbles and some screen shots of the feature in action have been posted. So far there’s not much new to the feature compared to Facebook’s Chat Heads – as you receive a message, you’ll get a visual notification on top of your screen, so you don’t have to leave the app you’re using.
Another thing the Bubbles feature has in common with Facebook’s Chat Heads you can drag and place the floating bubble to other parts of the screen. This feature looks to me like it will help conversations to move along faster and easier once completely implemented.