src/vs/base/browser/ui/tree/abstractTree.ts/TreeNodeListDragAndDrop/onDragStart
class TreeNodeListDragAndDrop:	onDragStart(data: IDragAndDropData, originalEvent: DragEvent): void {
		if (this.dnd.onDragStart) {
			this.dnd.onDragStart(asTreeDragAndDropData(data), originalEvent);
		}
	}