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

device/bluetooth/bluetooth_device.cc

Index: device/bluetooth/bluetooth_device.cc
diff --git a/device/bluetooth/bluetooth_device.cc b/device/bluetooth/bluetooth_device.cc
index 7d37591f5ea21483e15af7ab315436d3e8a6e70e..74672128f7bd8736046fe9c0a7e447fe409c4f91 100644
--- a/device/bluetooth/bluetooth_device.cc
+++ b/device/bluetooth/bluetooth_device.cc
@@ -29,13 +29,12 @@ BluetoothDevice::~BluetoothDevice() {
   DidDisconnectGatt();
 }
 
-BluetoothDevice::ConnectionInfo::ConnectionInfo()
-    : rssi(kUnknownPower),
-      transmit_power(kUnknownPower),
-      max_transmit_power(kUnknownPower) {}
+BluetoothDevice::ConnectionInfo::ConnectionInfo() {}
 
 BluetoothDevice::ConnectionInfo::ConnectionInfo(
-    int rssi, int transmit_power, int max_transmit_power)
+    const base::Optional<int8_t>& rssi,
+    const base::Optional<int8_t>& transmit_power,
+    const base::Optional<int8_t>& max_transmit_power)
     : rssi(rssi),
       transmit_power(transmit_power),
       max_transmit_power(max_transmit_power) {}