Add imgui golf mode overlay

Source/Core/VideoCommon/NetPlayGolfUI.h

@@ -0,0 +1,27 @@
+// Copyright 2019 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <memory>
+#include <string>
+
+namespace NetPlay
+{
+class NetPlayClient;
+}
+
+class NetPlayGolfUI
+{
+public:
+  explicit NetPlayGolfUI(std::shared_ptr<NetPlay::NetPlayClient> netplay_client);
+  ~NetPlayGolfUI() = default;
+
+  void Display();
+
+private:
+  std::weak_ptr<NetPlay::NetPlayClient> m_netplay_client;
+};
+
+extern std::unique_ptr<NetPlayGolfUI> g_netplay_golf_ui;