src/vs/platform/undoRedo/common/undoRedoService.ts/UndoRedoService/_getAffectedEditStacks
class UndoRedoService:	private _getAffectedEditStacks(element: WorkspaceStackElement): EditStackSnapshot {
		const affectedEditStacks: ResourceEditStack[] = [];
		for (const strResource of element.strResources) {
			affectedEditStacks.push(this._editStacks.get(strResource) || missingEditStack);
		}
		return new EditStackSnapshot(affectedEditStacks);
	}