bluetooth: Change GetInquiryTxPower and GetInquiryRSSI to return optional.

device/bluetooth/bluetooth_device_android.cc

Index: device/bluetooth/bluetooth_device_android.cc
diff --git a/device/bluetooth/bluetooth_device_android.cc b/device/bluetooth/bluetooth_device_android.cc
index bfd2ea642e2b0fe986f81ee2c3da181c455f43c0..15a2e92caa11dcced0b5224475118542e5d6e49a 100644
--- a/device/bluetooth/bluetooth_device_android.cc
+++ b/device/bluetooth/bluetooth_device_android.cc
@@ -139,14 +139,14 @@ bool BluetoothDeviceAndroid::IsConnecting() const {
   return false;
 }
 
-int16_t BluetoothDeviceAndroid::GetInquiryRSSI() const {
+base::Optional<int8_t> BluetoothDeviceAndroid::GetInquiryRSSI() const {
   NOTIMPLEMENTED();
-  return kUnknownPower;
+  return base::nullopt;
 }
 
-int16_t BluetoothDeviceAndroid::GetInquiryTxPower() const {
+base::Optional<int8_t> BluetoothDeviceAndroid::GetInquiryTxPower() const {
   NOTIMPLEMENTED();
-  return kUnknownPower;
+  return base::nullopt;
 }
 
 bool BluetoothDeviceAndroid::ExpectingPinCode() const {