Bluetooth: macOS: DidModifyServices can happens while scanning

device/bluetooth/bluetooth_remote_gatt_service_mac.h

 // 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.
 
 #ifndef DEVICE_BLUETOOTH_BLUETOOTH_REMOTE_GATT_SERVICE_MAC_H_
 #define DEVICE_BLUETOOTH_BLUETOOTH_REMOTE_GATT_SERVICE_MAC_H_
 
 #include <stdint.h>
 
 #include <unordered_map>
@@ skipping 78 matching lines @@
   base::scoped_nsobject<CBService> service_;
   // Map of characteristics, keyed by characteristic identifier.
   std::unordered_map<std::string,
                      std::unique_ptr<BluetoothRemoteGattCharacteristicMac>>
       gatt_characteristic_macs_;
   bool is_primary_;
   // Service identifier.
   std::string identifier_;
   // Service UUID.
   BluetoothUUID uuid_;
-  // Is true if the characteristics has been discovered.
+  // Is true if the characteristics has been discovered and
+  // discovery_pending_count_ is 0.
   bool is_discovery_complete_;
+  // Increased each time DiscoverCharacteristics() is called. And decreased when
+  // DidDiscoverCharacteristics() is called.
+  int discovery_pending_count_;
 
   DISALLOW_COPY_AND_ASSIGN(BluetoothRemoteGattServiceMac);
 };
 
 // Stream operator for logging.
 DEVICE_BLUETOOTH_EXPORT std::ostream& operator<<(
     std::ostream& out,
     const BluetoothRemoteGattServiceMac& service);
 
 }  // namespace device
 
 #endif  // DEVICE_BLUETOOTH_BLUETOOTH_REMOTE_GATT_SERVICE_MAC_H_