Allow background activity launch by drag notification

Drag notification to launch activity is aborted since the app is not
visible.

This CL adds the background activity allowed flag to make activity
launches successful.

Bug: 237985674
Test: Drag the notification to home. Check the activity is launched.
Change-Id: I6513e7d5d7b17c4a41c32316fd7504fe1bf2e793
2 files changed