src/vs/workbench/browser/parts/views/treeView.ts/TreeRenderer/getFileKind
class TreeRenderer:	private getFileKind(node: ITreeItem): FileKind {
		if (node.themeIcon) {
			switch (node.themeIcon.id) {
				case FileThemeIcon.id:
					return FileKind.FILE;
				case FolderThemeIcon.id:
					return FileKind.FOLDER;
			}
		}
		return node.collapsibleState === TreeItemCollapsibleState.Collapsed || node.collapsibleState === TreeItemCollapsibleState.Expanded ? FileKind.FOLDER : FileKind.FILE;
	}