bluetooth: Change GetInquiryTxPower and GetInquiryRSSI to return optional.

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 8b4c5b0018f11595db363041b4df3fb9814c5371..bc346e835ae91e6842a660fbda33dd751aa432b7 100644
--- a/device/bluetooth/bluetooth_device.h
+++ b/device/bluetooth/bluetooth_device.h
@@ -305,15 +305,13 @@ class DEVICE_BLUETOOTH_EXPORT BluetoothDevice {
   virtual UUIDList GetUUIDs() const;
 
   // The received signal strength, in dBm. This field is avaliable and valid
-  // only during discovery. If not during discovery, or RSSI wasn't reported,
-  // this method will return |kUnknownPower|.
-  virtual int16_t GetInquiryRSSI() const = 0;
+  // only during discovery.
+  virtual base::Optional<int8_t> GetInquiryRSSI() const = 0;
 
   // The transmitted power level. This field is avaliable only for LE devices
   // that include this field in AD. It is avaliable and valid only during
-  // discovery. If not during discovery, or TxPower wasn't reported, this
-  // method will return |kUnknownPower|.
-  virtual int16_t GetInquiryTxPower() const = 0;
+  // discovery.
+  virtual base::Optional<int8_t> GetInquiryTxPower() const = 0;
 
   // The ErrorCallback is used for methods that can fail in which case it
   // is called, in the success case the callback is simply not called.