src/vs/workbench/browser/dnd.ts/CompositeDragAndDropObserver/readDragData
class CompositeDragAndDropObserver:	private readDragData(type: ViewType): CompositeDragAndDropData | undefined {
		if (this.transferData.hasData(type === 'view' ? DraggedViewIdentifier.prototype : DraggedCompositeIdentifier.prototype)) {
			const data = this.transferData.getData(type === 'view' ? DraggedViewIdentifier.prototype : DraggedCompositeIdentifier.prototype);
			if (data && data[0]) {
				return new CompositeDragAndDropData(type, data[0].id);
			}
		}

		return undefined;
	}