bluetooth: Return int8_t and use -128 for unknown tx power.

device/bluetooth/dbus/bluetooth_device_client.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef DEVICE_BLUETOOTH_DBUS_BLUETOOTH_DEVICE_CLIENT_H_
 #define DEVICE_BLUETOOTH_DBUS_BLUETOOTH_DEVICE_CLIENT_H_
 
 #include <stdint.h>
 
 #include <string>
 #include <vector>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/observer_list.h"
+#include "base/optional.h"
 #include "base/values.h"
 #include "dbus/object_path.h"
 #include "dbus/property.h"
 #include "device/bluetooth/bluetooth_export.h"
 #include "device/bluetooth/dbus/bluez_dbus_client.h"
 
 namespace bluez {
 
 // BluetoothDeviceClient is used to communicate with objects representing
 // remote Bluetooth Devices.
@@ skipping 152 matching lines @@
                     const ErrorCallback& error_callback) = 0;
 
   // Cancels an in-progress pairing with the device with object path
   // |object_path| initiated by Pair().
   virtual void CancelPairing(const dbus::ObjectPath& object_path,
                              const base::Closure& callback,
                              const ErrorCallback& error_callback) = 0;
 
   // The callback invoked for a successful GetConnInfo API call with the
   // RSSI, TX power, and maximum TX power of the current connection.
-  typedef base::Callback<void(int16_t rssi,
-                              int16_t transmit_power,
-                              int16_t max_transmit_power)> ConnInfoCallback;
+  typedef base::Callback<void(
+      const base::Optional<int16_t>& rssi,
+      const base::Optional<int16_t>& transmit_power,
+      const base::Optional<int16_t>& max_transmit_power)>
+      ConnInfoCallback;
 
   // Returns the RSSI, TX power, and maximum TX power of a connection to the
   // device with object path |object_path|. If the device is not connected, then
   // an error will be returned.
   virtual void GetConnInfo(const dbus::ObjectPath& object_path,
                            const ConnInfoCallback& callback,
                            const ErrorCallback& error_callback) = 0;
 
   // Creates the instance.
   static BluetoothDeviceClient* Create();
 
   // Constants used to indicate exceptional error conditions.
   static const char kNoResponseError[];
   static const char kUnknownDeviceError[];
 
  protected:
   BluetoothDeviceClient();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(BluetoothDeviceClient);
 };
 
 }  // namespace bluez
 
 #endif  // DEVICE_BLUETOOTH_DBUS_BLUETOOTH_DEVICE_CLIENT_H_