Use Borderless Window setting doesn't work on Mac

if( Definition->IsRegularWindow )
{
	if( Definition->HasCloseButton )
	{
		WindowStyle = NSWindowStyleMaskClosable;
	}
 
	// In order to support rounded, shadowed windows set the window to be titled - we'll set the content view to cover the whole window
	WindowStyle |= NSWindowStyleMaskTitled | (FPlatformMisc::IsRunningOnMavericks() ? NSWindowStyleMaskTexturedBackground : NSWindowStyleMaskFullSizeContentView);
	
	if( Definition->SupportsMinimize )
	{
		WindowStyle |= NSWindowStyleMaskMiniaturizable;
	}
	if( Definition->SupportsMaximize || Definition->HasSizingFrame )
	{
		WindowStyle |= NSWindowStyleMaskResizable;
	}
}
else
{
	WindowStyle = NSWindowStyleMaskBorderless;
}