code: @Override
      public DescribeSourceRegionsResult describeSourceRegions(DescribeSourceRegionsRequest request) {
          request = beforeClientExecution(request);
          return executeDescribeSourceRegions(request);
      }
docs: <p>
  Returns a list of the source AWS Regions where the current AWS Region can create a Read Replica or copy a DB
  snapshot from. This API action supports pagination.
  </p>
  
  @param describeSourceRegionsRequest
  @return Result of the DescribeSourceRegions operation returned by the service.
  @sample AmazonRDS.DescribeSourceRegions
  @see <a href="http://docs.aws.amazon.com/goto/WebAPI/rds-2014-10-31/DescribeSourceRegions" target="_top">AWS API
  Documentation</a>