Feature Request: Delay transition to background mode

[davidgyoung]

Expected behavior

It is often desired for Apps to continue scanning after transition to the background to the extent allowed by the operating system, especially on Android 8+ where background scanning (without a foreground service) is limited to once every 15 minute job scheduler events.

Actual behavior

When using BackgroundPowerSaver, The library stops scanning at foreground rates immediately after the app goes to the background, causing scans to be delayed for up to 15 minutes on Android 8+, even though the operating system would allow scans for up to 10 minutes after transitioning to the background.

Steps to reproduce this behavior

Run the reference app on an Android 8 device, go to the ranging screen, put the app to the background. Ranging updates immediately stop.

Mobile device model and OS version

Any

Android Beacon Library version

2.15

Proposal

Add a configurable delay in switching to background scan periods after the app is put to the background. On Android 8+ up to 10 minutes of background running time is allowed, so this delay could be up to 10 minutes. This would address #666