src/vs/workbench/api/common/extHostDocumentSaveParticipant.ts/ExtHostDocumentSaveParticipant/getOnWillSaveTextDocumentEvent
class ExtHostDocumentSaveParticipant:	getOnWillSaveTextDocumentEvent(extension: IExtensionDescription): Event<vscode.TextDocumentWillSaveEvent> {
		return (listener, thisArg, disposables) => {
			const remove = this._callbacks.push([listener, thisArg, extension]);
			const result = { dispose: remove };
			if (Array.isArray(disposables)) {
				disposables.push(result);
			}
			return result;
		};
	}