BluetoothAdapter::DevicePairedChanged is confusing. The comment says:

    // This function is implemented for ChromeOS only, and the support for
    // Android, MaxOS and Windows should be added on demand in the future.

But the function is wrapped in:
  #if defined(OS_CHROMEOS) || defined(OS_LINUX)

Is it intentionally enabled on Linux (rather than Chrome OS only)?

If so, the defined(OS_CHROMEOS) is redundant -- Chrome OS implies Linux.

(There are a bunch of repeats of this comment and #ifdef as the function is used or overridden in some places.

https://cs.chromium.org/chromium/src/device/bluetooth/bluetooth_adapter.h?type=cs&q=DevicePairedChanged&sq=package:chromium&l=125