Implement create attribute API functions for BTLE.

device/bluetooth/bluetooth_adapter_mac.h

Index: device/bluetooth/bluetooth_adapter_mac.h
diff --git a/device/bluetooth/bluetooth_adapter_mac.h b/device/bluetooth/bluetooth_adapter_mac.h
index 1491c1c026223dd6d95627a90d474491539c0e06..b6b55782929b4f1a998687c010c2fcd197a41170 100644
--- a/device/bluetooth/bluetooth_adapter_mac.h
+++ b/device/bluetooth/bluetooth_adapter_mac.h
@@ -85,6 +85,8 @@ class DEVICE_BLUETOOTH_EXPORT BluetoothAdapterMac
       std::unique_ptr<BluetoothAdvertisement::Data> advertisement_data,
       const CreateAdvertisementCallback& callback,
       const CreateAdvertisementErrorCallback& error_callback) override;
+  BluetoothLocalGattService* GetGattService(
+      const std::string& identifier) const override;
 
   // BluetoothDiscoveryManagerMac::Observer overrides:
   void ClassicDeviceFound(IOBluetoothDevice* device) override;