What is "DockArea.GetBorderSize()"?

I have created a 3D voxel terrain generator and have been trying to optimize it. However my game freezes for a moment sometimes when generating chunks. I found out its DockArea.GetBorderSize(). What it is and how to fix this? Didn’t find ANY info via Google about it.

Picture of profiler

EDIT: Picture seems to be scaled down… Heres original.

Hi I’m not 100% sure but i think this is caused by the Garbage Collector.