src/vs/workbench/contrib/markers/browser/markersView.ts/MarkersTree/getVisibleItemCount
class MarkersTree:	getVisibleItemCount(): number {
		let filtered = 0;
		const root = this.getNode();

		for (const resourceMarkerNode of root.children) {
			for (const markerNode of resourceMarkerNode.children) {
				if (resourceMarkerNode.visible && markerNode.visible) {
					filtered++;
				}
			}
		}

		return filtered;
	}