Bluetooth: macOS: DidModifyServices can happens while scanning

device/bluetooth/bluetooth_remote_gatt_service_mac.h

Index: device/bluetooth/bluetooth_remote_gatt_service_mac.h
diff --git a/device/bluetooth/bluetooth_remote_gatt_service_mac.h b/device/bluetooth/bluetooth_remote_gatt_service_mac.h
index 1c5d1c834def1b9c6a67a83ebb618d6b67f85078..832e41d051712d4c4adce2a3e78f174d1c5fe830 100644
--- a/device/bluetooth/bluetooth_remote_gatt_service_mac.h
+++ b/device/bluetooth/bluetooth_remote_gatt_service_mac.h
@@ -96,8 +96,12 @@ class DEVICE_BLUETOOTH_EXPORT BluetoothRemoteGattServiceMac
   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);
 };