bluetooth: Change GetInquiryTxPower and GetInquiryRSSI to return optional.

device/bluetooth/bluetooth_classic_device_mac.mm

Index: device/bluetooth/bluetooth_classic_device_mac.mm
diff --git a/device/bluetooth/bluetooth_classic_device_mac.mm b/device/bluetooth/bluetooth_classic_device_mac.mm
index eaeba2c6bc9406628770a6edf9bf7e6da2f1df17..0e471e6e339761f048614f6db444f91277fdc490 100644
--- a/device/bluetooth/bluetooth_classic_device_mac.mm
+++ b/device/bluetooth/bluetooth_classic_device_mac.mm
@@ -148,13 +148,12 @@ BluetoothDevice::UUIDList BluetoothClassicDeviceMac::GetUUIDs() const {
   return uuids;
 }
 
-int16_t BluetoothClassicDeviceMac::GetInquiryRSSI() const {
-  return kUnknownPower;
+base::Optional<int8_t> BluetoothClassicDeviceMac::GetInquiryRSSI() const {
+  return base::nullopt;
 }
 
-int16_t BluetoothClassicDeviceMac::GetInquiryTxPower() const {
-  NOTIMPLEMENTED();
-  return kUnknownPower;
+base::Optional<int8_t> BluetoothClassicDeviceMac::GetInquiryTxPower() const {
+  return base::nullopt;
 }
 
 bool BluetoothClassicDeviceMac::ExpectingPinCode() const {