Implement create attribute API functions for BTLE.

device/bluetooth/bluetooth_local_gatt_service.h

Index: device/bluetooth/bluetooth_local_gatt_service.h
diff --git a/device/bluetooth/bluetooth_local_gatt_service.h b/device/bluetooth/bluetooth_local_gatt_service.h
index 668985ae99fc05614a004c92782fcd0ad7058392..b78336ea0745bbc980c9afad304dcaad9e1141c3 100644
--- a/device/bluetooth/bluetooth_local_gatt_service.h
+++ b/device/bluetooth/bluetooth_local_gatt_service.h
@@ -150,6 +150,9 @@ class DEVICE_BLUETOOTH_EXPORT BluetoothLocalGattService
   virtual void Unregister(const base::Closure& callback,
                           const ErrorCallback& error_callback) = 0;
 
+  virtual BluetoothLocalGattCharacteristic* GetCharacteristic(
+      const std::string& identifier) = 0;
+
  protected:
   BluetoothLocalGattService();
   ~BluetoothLocalGattService() override;