src/vs/workbench/contrib/notebook/browser/notebookServiceImpl.ts/NotebookService/_registerProviderData
class NotebookService:	private _registerProviderData(viewType: string, data: SimpleNotebookProviderInfo | ComplexNotebookProviderInfo): IDisposable {
		if (this._notebookProviders.has(viewType)) {
			throw new Error(`notebook provider for viewtype '${viewType}' already exists`);
		}
		this._notebookProviders.set(viewType, data);
		this._onAddViewType.fire(viewType);
		return toDisposable(() => {
			this._onWillRemoveViewType.fire(viewType);
			this._notebookProviders.delete(viewType);
		});
	}