where is taskbar grouped button arrow??

Hi everyone.
 
I'm trying to get closer to se7en superbar without 3rd-party programs. So i need to know where in windows could be little white, down heading arrow, used on taskbar when you have ,,Taskbar Button Grouping'' active
 

 
I've been looking in ms styles dll, explorer.exe and shell32.dll with resHacker, but didn't found anything 
 
So if someone here could give a clue how to find it or who could know it tell i to me.
 
Thanks a lot.