Source/modules/bluetooth implements the renderer process details and bindings for the Web Bluetooth specification. It uses the Web Bluetooth Service mojom to communicate with the Web Bluetooth Service.
There isn't much support for GATT over BR/EDR from neither platforms nor devices so performing a Dual scan will find devices that the API is not able to interact with. To avoid wasting power and confusing users with devices they are not able to interact with, navigator.bluetooth.requestDevice performs an LE-only Scan.
Bluetooth layout tests in
LayoutTests/bluetooth/ rely on fake Bluetooth implementation classes constructed in
device/bluetooth API layer.
See also the Web Bluetooth Fuzzer.