src/vs/workbench/contrib/notebook/browser/notebook.contribution.ts/NotebookEditorSerializer/serialize
class NotebookEditorSerializer:	serialize(input: EditorInput): string {
		assertType(input instanceof NotebookEditorInput);
		const data: SerializedNotebookEditorData = {
			resource: input.resource,
			viewType: input.viewType
		};
		return JSON.stringify(data);
	}