Add OpenVR SDK to third_party

third_party/openvr/src/src/ivrclientcore.h

Index: third_party/openvr/src/src/ivrclientcore.h
diff --git a/third_party/openvr/src/src/ivrclientcore.h b/third_party/openvr/src/src/ivrclientcore.h
new file mode 100644
index 0000000000000000000000000000000000000000..49c563e805642699dd8a577f2c7499acf026b110
--- /dev/null
+++ b/third_party/openvr/src/src/ivrclientcore.h
@@ -0,0 +1,35 @@
+//========= Copyright Valve Corporation ============//
+#pragma once
+
+namespace vr
+{
+
+class IVRClientCore
+{
+public:
+	/** Initializes the system */
+	virtual EVRInitError Init( vr::EVRApplicationType eApplicationType ) = 0;
+
+	/** cleans up everything in vrclient.dll and prepares the DLL to be unloaded */
+	virtual void Cleanup() = 0;
+
+	/** checks to see if the specified interface/version is supported in this vrclient.dll */
+	virtual EVRInitError IsInterfaceVersionValid( const char *pchInterfaceVersion ) = 0;
+
+	/** Retrieves any interface from vrclient.dll */
+	virtual void *GetGenericInterface( const char *pchNameAndVersion, EVRInitError *peError ) = 0;
+
+	/** Returns true if any driver has an HMD attached. Can be called outside of Init/Cleanup */
+	virtual bool BIsHmdPresent() = 0;
+
+	/** Returns an english error string from inside vrclient.dll which might be newer than the API DLL */
+	virtual const char *GetEnglishStringForHmdError( vr::EVRInitError eError ) = 0;
+
+	/** Returns an error symbol from inside vrclient.dll which might be newer than the API DLL */
+	virtual const char *GetIDForVRInitError( vr::EVRInitError eError ) = 0;
+};
+
+static const char * const IVRClientCore_Version = "IVRClientCore_002";
+
+
+}