Added original SDK code for Alien Swarm.

public/vgui/KeyCode.h

@@ -0,0 +1,24 @@
+//===== Copyright <20> 1996-2005, Valve Corporation, All rights reserved. ======//
+//
+// Purpose: this is a map for virtual key codes
+//			virtual key codes may exist outside this range for other languages
+// NOTE: Button codes also contain mouse codes, but we won't worry about that
+//
+// $NoKeywords: $
+//===========================================================================//
+
+#ifndef KEYCODE_H
+#define KEYCODE_H
+
+#ifdef _WIN32
+#pragma once
+#endif
+
+#include "inputsystem/ButtonCode.h"
+
+namespace vgui
+{
+typedef ButtonCode_t KeyCode;
+}
+
+#endif // KEYCODE_H