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

device/bluetooth/dbus/bluetooth_device_client.cc

Index: device/bluetooth/dbus/bluetooth_device_client.cc
diff --git a/device/bluetooth/dbus/bluetooth_device_client.cc b/device/bluetooth/dbus/bluetooth_device_client.cc
index 11626f505a7be6f202afbdd338256831215fccb7..05adc0361d2d517df7d8fe80a09f9e4d4c7ba9b5 100644
--- a/device/bluetooth/dbus/bluetooth_device_client.cc
+++ b/device/bluetooth/dbus/bluetooth_device_client.cc
@@ -7,6 +7,7 @@
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/macros.h"
+#include "base/optional.h"
 #include "base/stl_util.h"
 #include "dbus/bus.h"
 #include "dbus/message.h"
@@ -16,13 +17,6 @@
 
 namespace bluez {
 
-namespace {
-
-// Value returned for the the RSSI or TX power if it cannot be read.
-const int kUnknownPower = 127;
-
-}  // namespace
-
 const char BluetoothDeviceClient::kNoResponseError[] =
     "org.chromium.Error.NoResponse";
 const char BluetoothDeviceClient::kUnknownDeviceError[] =
@@ -320,22 +314,24 @@ class BluetoothDeviceClientImpl : public BluetoothDeviceClient,
   // Called when a response for the GetConnInfo method is received.
   void OnGetConnInfoSuccess(const ConnInfoCallback& callback,
                             dbus::Response* response) {
-    int16_t rssi = kUnknownPower;
-    int16_t transmit_power = kUnknownPower;
-    int16_t max_transmit_power = kUnknownPower;
-
     if (!response) {
       LOG(ERROR) << "GetConnInfo succeeded, but no response received.";
-      callback.Run(rssi, transmit_power, max_transmit_power);
+      callback.Run(base::nullopt /* rssi */, base::nullopt /* transmit_power */,
+                   base::nullopt /* max_tx_power */);
       return;
     }
 
+    int16_t rssi;
+    int16_t transmit_power;
+    int16_t max_transmit_power;
+
     dbus::MessageReader reader(response);
     if (!reader.PopInt16(&rssi) || !reader.PopInt16(&transmit_power) ||
         !reader.PopInt16(&max_transmit_power)) {
       LOG(ERROR) << "Arguments for GetConnInfo invalid.";
     }
-    callback.Run(rssi, transmit_power, max_transmit_power);
+    callback.Run(base::make_optional(rssi), base::make_optional(transmit_power),
+                 base::make_optional(max_transmit_power));
   }
 
   // Called when a response for a failed method call is received.