Expose device RSSI and Tx power via the chrome.bluetooth API.

device/bluetooth/bluetooth_device.h

Index: device/bluetooth/bluetooth_device.h
diff --git a/device/bluetooth/bluetooth_device.h b/device/bluetooth/bluetooth_device.h
index 7a29cac6235287c51a90fba637199bc483b8d22f..5a8380328425cbfb5667b02e74d75fb637a71499 100644
--- a/device/bluetooth/bluetooth_device.h
+++ b/device/bluetooth/bluetooth_device.h
@@ -227,6 +227,11 @@ class BluetoothDevice {
   // DEVICE_PERIPHERAL.
   DeviceType GetDeviceType() const;
 
+  // Returns the "received signal strength indication" (RSSI) of the device.
+  // The RSSI is a measurement of the power present in a received radio signal.
+  // Larger (typically, less negative) values indicate a stronger signal.
+  virtual int GetRSSI() const = 0;

[keybuk, 2014/04/23 08:59:19]

Is this the RSSI of inquiry/AD packets - or is this the RSSI of the connection
to the device?

If the latter, then this will require a round-trip to the controller so should
be a method with a callback

[Ilya Sherman, 2014/04/24 06:45:16]

It's the latter.  Do you want me to include a pair of callbacks -- one for
success and one for failure?  FWIW, on Mac, the call is synchronous.  Maybe it
makes sense not to add callbacks until we implement this on a platform that
needs them?  Of course, if you prefer that I add callbacks now, I'm happy to do
that as well.

[keybuk, 2014/04/24 11:25:52]

If synchronous then there should definitely be a callback, you cannae block the
UI thread cap'n

+
   // Indicates whether the device is known to support pairing based on its
   // device class and address.
   bool IsPairable() const;