src/vs/workbench/services/search/node/fileSearch.ts/FileWalker/initDirectoryTree
class FileWalker:	private initDirectoryTree(): IDirectoryTree {
		const tree: IDirectoryTree = {
			rootEntries: [],
			pathToEntries: Object.create(null)
		};
		tree.pathToEntries['.'] = tree.rootEntries;
		return tree;
	}