src/vs/workbench/api/common/extHostNotebookDocument.ts/ExtHostCell/apiCell
class ExtHostCell:	get apiCell(): vscode.NotebookCell {
		if (!this._apiCell) {
			const that = this;
			const data = this._extHostDocument.getDocument(this.uri);
			if (!data) {
				throw new Error(`MISSING extHostDocument for notebook cell: ${this.uri}`);
			}
			this._apiCell = Object.freeze<vscode.NotebookCell>({
				get index() { return that.notebook.getCellIndex(that); },
				notebook: that.notebook.apiNotebook,
				kind: extHostTypeConverters.NotebookCellKind.to(this._cellData.cellKind),
				document: data.document,
				get mime() { return that._mime; },
				set mime(value: string | undefined) { that._mime = value; },
				get outputs() { return that._outputs.slice(0); },
				get metadata() { return that._metadata; },
				get executionSummary() { return that._previousResult; }
			});
		}
		return this._apiCell;
	}