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

components/arc/bluetooth/arc_bluetooth_bridge.cc

 // Copyright 2016 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.
 
 #include "components/arc/bluetooth/arc_bluetooth_bridge.h"
 
 #include <fcntl.h>
 #include <stddef.h>
 
 #include <iomanip>
@@ skipping 555 matching lines @@
     properties.push_back(std::move(btp));
   }
   if (type == mojom::BluetoothPropertyType::ALL ||
       type == mojom::BluetoothPropertyType::REMOTE_FRIENDLY_NAME) {
     mojom::BluetoothPropertyPtr btp = mojom::BluetoothProperty::New();
     btp->set_bdname(mojo::String::From(base::UTF16ToUTF8(device->GetName())));
     properties.push_back(std::move(btp));
   }
   if (type == mojom::BluetoothPropertyType::ALL ||
       type == mojom::BluetoothPropertyType::REMOTE_RSSI) {
-    mojom::BluetoothPropertyPtr btp = mojom::BluetoothProperty::New();
-    btp->set_remote_rssi(device->GetInquiryRSSI());
-    properties.push_back(std::move(btp));
+    if (device->GetInquiryRSSI()) {
+      mojom::BluetoothPropertyPtr btp = mojom::BluetoothProperty::New();
+      btp->set_remote_rssi(device->GetInquiryRSSI().value());
+      properties.push_back(std::move(btp));
+    }
   }
   // TODO(smbarber): Add remote version info
 
   return properties;
 }
 
 mojo::Array<mojom::BluetoothPropertyPtr>
 ArcBluetoothBridge::GetAdapterProperties(
     mojom::BluetoothPropertyType type) const {
   mojo::Array<mojom::BluetoothPropertyPtr> properties;
@@ skipping 119 matching lines @@
     // to
     // make sure the bond state machine on Android is ready to take the
     // pair-done event. Otherwise the pair-done event will be dropped as an
     // invalid change of paired status.
     OnPairing(addr->Clone());
     OnPairedDone(std::move(addr));
   }
 }
 
 }  // namespace arc