src/vs/base/browser/ui/grid/gridview.ts/GridView/getViewMap
class GridView:	getViewMap(map: Map<IView, HTMLElement>, node?: Node): void {
		if (!node) {
			node = this.root;
		}

		if (node instanceof BranchNode) {
			node.children.forEach(child => this.getViewMap(map, child));
		} else {
			map.set(node.view, node.element);
		}
	}