What steps will reproduce the problem?
0. Run Chrome with logging enabled:
 --enable-logging --v=1  --enable-logging=stderr
1. https://googlechrome.github.io/samples/web-bluetooth/device-information-characteristics.html
2. Click button to start scanning for devices
3. Cancel the dialog

Scanning continues.

This [patch] includes a VLOG in BluetoothAdapterMac::ClassicDeviceAdded, which will show the scanning in output:

https://codereview.chromium.org/2282763004/