Prompt users if they want to quit on back button press

[bluemarvin]

Hardware

WaveVR and Daydream

Steps to Reproduce

1. Launch FxR
2. Press back button on controller

Current Behavior

FxR exits to device home environment.

Expected Behavior

FxR should prompt user if they want to exit FxR

Possible Solution

On the Go, when the user pushed the back button with no more history, it will trigger a system UI asking if the user wants to exit or continue. On the Daydream and WaveVR the user is dumped back into the home env with out prompting which can be annoying when mashing the back button one too many times.

[keianhzo]

@bluemarvin From my experience no Daydream app use the Back button for exiting, you have to press Home to exit the app. The Back button is only used to go back inside the app (Chrome doesn't even use it for going back in history).

Maybe just not using the back button for exiting in Daydream would be a more Daydream-standard way of dealing with this.

All this in Daydream clip-ins, not sure on Mirage Solo.

[philip-lamb]

On WaveVR and Daydream we should trap and discard any back button presses that would otherwise exit the app, as the UI standard on these platforms is to require the use of the system menu to exit applications.