code: @Override
      public StartSchemaExtensionResult startSchemaExtension(StartSchemaExtensionRequest request) {
          request = beforeClientExecution(request);
          return executeStartSchemaExtension(request);
      }
docs: <p>
  Applies a schema extension to a Microsoft AD directory.
  </p>
  
  @param startSchemaExtensionRequest
  @return Result of the StartSchemaExtension operation returned by the service.
  @throws DirectoryUnavailableException
  The specified directory is unavailable or could not be found.
  @throws EntityDoesNotExistException
  The specified entity could not be found.
  @throws InvalidParameterException
  One or more parameters are not valid.
  @throws SnapshotLimitExceededException
  The maximum number of manual snapshots for the directory has been reached. You can use the
  <a>GetSnapshotLimits</a> operation to determine the snapshot limits for a directory.
  @throws ClientException
  A client exception has occurred.
  @throws ServiceException
  An exception has occurred in AWS Directory Service.
  @sample AWSDirectoryService.StartSchemaExtension
  @see <a href="http://docs.aws.amazon.com/goto/WebAPI/ds-2015-04-16/StartSchemaExtension" target="_top">AWS API
  Documentation</a>