Bluetooth: macOS: DidModifyServices can happens while scanning

device/bluetooth/bluetooth_remote_gatt_characteristic_mac.h

Index: device/bluetooth/bluetooth_remote_gatt_characteristic_mac.h
diff --git a/device/bluetooth/bluetooth_remote_gatt_characteristic_mac.h b/device/bluetooth/bluetooth_remote_gatt_characteristic_mac.h
index 384c2658f4462b3b0ff67fc66dfc30d479e1b00d..2fac4e449e026caf0c28601d957fea7932bcfdc2 100644
--- a/device/bluetooth/bluetooth_remote_gatt_characteristic_mac.h
+++ b/device/bluetooth/bluetooth_remote_gatt_characteristic_mac.h
@@ -99,8 +99,12 @@ class DEVICE_BLUETOOTH_EXPORT BluetoothRemoteGattCharacteristicMac
   // Returns BluetoothRemoteGattDescriptorMac from CBDescriptor.
   BluetoothRemoteGattDescriptorMac* GetBluetoothRemoteGattDescriptorMac(
       CBDescriptor* cb_descriptor) const;
-  // Is true if the characteristic has been discovered with all its descriptors.
+  // Is true if the characteristic has been discovered with all its descriptors
+  // and discovery_pending_count_ is 0.
   bool is_discovery_complete_;
+  // Increased each time DiscoverDescriptors() is called. And decreased when
+  // DidDiscoverDescriptors() is called.
+  int discovery_pending_count_;
   // gatt_service_ owns instances of this class.
   BluetoothRemoteGattServiceMac* gatt_service_;
   // A characteristic from CBPeripheral.services.characteristics.