bluetooth: Add test for background permission requests

This change adds a test for sites which attempt to show the Web
Bluetooth permission prompt while they are in the background. This
scenario exposed a use-after-free which was fixed without a
corresponding test in r829523.

This exposed a more general issue that in this scenario the Promise
returned by requestDevice() would never resolve. Fixing this requires
making sure that the chooser event callback is executed when the
controller is destroyed and fixing the resulting reentrancy issues. To
make this simpler the success and failure callbacks passed to
BluetoothDeviceChooserController have been merged.

Bug: 730593,1149692
Change-Id: I9042e2c636322ad3ab2dff04050b45a5c3ec2fbb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2858256
Commit-Queue: Reilly Grant <reillyg@chromium.org>
Reviewed-by: Mike Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#877638}