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

components/proximity_auth/metrics.cc

Index: components/proximity_auth/metrics.cc
diff --git a/components/proximity_auth/metrics.cc b/components/proximity_auth/metrics.cc
index b8ceb1f676129dbdc69bb2ee1cea461ca5ada174..915957bd8cc050b4c8e845da74271e4a97fb80fc 100644
--- a/components/proximity_auth/metrics.cc
+++ b/components/proximity_auth/metrics.cc
@@ -14,6 +14,7 @@
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/sparse_histogram.h"
 #include "base/sys_byteorder.h"
+#include "device/bluetooth/bluetooth_device.h"
 
 namespace proximity_auth {
 namespace metrics {
@@ -46,10 +47,9 @@ int32_t HashDeviceModelName(const std::string& name) {
 }  // namespace
 
 const char kUnknownDeviceModel[] = "Unknown";
-const int kUnknownProximityValue = 127;
 
 void RecordAuthProximityRollingRssi(int rolling_rssi) {
-  if (rolling_rssi != kUnknownProximityValue)
+  if (rolling_rssi != device::BluetoothDevice::kUnknownRSSI)
     rolling_rssi = std::min(50, std::max(-100, rolling_rssi));
 
   UMA_HISTOGRAM_SPARSE_SLOWLY("EasyUnlock.AuthProximity.RollingRssi",
@@ -57,7 +57,7 @@ void RecordAuthProximityRollingRssi(int rolling_rssi) {
 }
 
 void RecordAuthProximityTransmitPowerDelta(int transmit_power_delta) {
-  if (transmit_power_delta != kUnknownProximityValue)
+  if (transmit_power_delta != device::BluetoothDevice::kUnknownTxPower)
     transmit_power_delta = std::min(50, std::max(-100, transmit_power_delta));
 
   UMA_HISTOGRAM_SPARSE_SLOWLY("EasyUnlock.AuthProximity.TransmitPowerDelta",