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

components/proximity_auth/proximity_monitor_impl.cc

Index: components/proximity_auth/proximity_monitor_impl.cc
diff --git a/components/proximity_auth/proximity_monitor_impl.cc b/components/proximity_auth/proximity_monitor_impl.cc
index e6d8d7b2c01413eaae8acf6cdcec6508303b93ed..c1d290f604a07dd7f5c243376acd28409e26a45f 100644
--- a/components/proximity_auth/proximity_monitor_impl.cc
+++ b/components/proximity_auth/proximity_monitor_impl.cc
@@ -87,13 +87,13 @@ bool ProximityMonitorImpl::IsInRssiRange() const {
 void ProximityMonitorImpl::RecordProximityMetricsOnAuthSuccess() {
   double rssi_rolling_average = rssi_rolling_average_
                                     ? *rssi_rolling_average_
-                                    : metrics::kUnknownProximityValue;
+                                    : device::BluetoothDevice::kUnknownRSSI;
 
   int last_transmit_power_delta =
       last_transmit_power_reading_
           ? (last_transmit_power_reading_->transmit_power -
              last_transmit_power_reading_->max_transmit_power)
-          : metrics::kUnknownProximityValue;
+          : device::BluetoothDevice::kUnknownTxPower;
 
   // If no zero RSSI value has been read, then record an overflow.
   base::TimeDelta time_since_last_zero_rssi;
@@ -204,9 +204,9 @@ void ProximityMonitorImpl::OnConnectionInfo(
     return;
   }
 
-  if (connection_info.rssi != BluetoothDevice::kUnknownPower &&
-      connection_info.transmit_power != BluetoothDevice::kUnknownPower &&
-      connection_info.max_transmit_power != BluetoothDevice::kUnknownPower) {
+  if (connection_info.rssi != BluetoothDevice::kUnknownRSSI &&
+      connection_info.transmit_power != BluetoothDevice::kUnknownTxPower &&
+      connection_info.max_transmit_power != BluetoothDevice::kUnknownTxPower) {
     AddSample(connection_info);
   } else {
     PA_LOG(WARNING) << "[Proximity] Unkown values received from API: "