Extend our OSD class to support callbacks on init, onframe, and shutdown.

Source/Core/VideoCommon/Src/OnScreenDisplay.h

@@ -26,6 +26,18 @@ void AddMessage(const char* str, u32 ms = 2000);
 void DrawMessages(); // draw the current messages on the screen. Only call once per frame.
 void ClearMessages();
 
+// On-screen callbacks
+enum CallbackType
+{
+	OSD_INIT = 0,
+	OSD_ONFRAME,
+	OSD_SHUTDOWN
+};
+typedef void(*CallbackPtr)(u32);
+
+void AddCallback(CallbackType OnType, CallbackPtr FuncPtr, u32 UserData);
+
+void DoCallbacks(CallbackType OnType);
 }  // namespace
 
 #endif // _OSD_H_