I have considerate to show the error message in the Bluetooth app. But, there are two reason that I'm not able to do it.
`showDevicePaired(false, option)` will trigger the error message.
1. After requested `var req = defaultAdapter.pair(device.address);`, the `req.onerror` might notify the error.
2. `defaultAdapter.onpairedstatuschanged` will trigger the error message.

The two case are handled in Settings app. It's more relative with user interaction in Settings. Beside, Bluetooth app will do `window.close` after a user confirmed via the pairing dialog. Bluetooth app have no way to receive the error message now.