public DocumentProcessor.Progress call(Processing processing) {
        try {
            int numDocs = processing.getDocumentOperations().size();
            schemaMapProcessing(processing);
            long startTime = SystemTimer.INSTANCE.milliTime();
            DocumentProcessor.Progress retval = processor.process(processing);
            long procTime = SystemTimer.INSTANCE.milliTime() - startTime;
            updateMetrics(procTime, numDocs);
            return retval;
        } finally {
            unwrapSchemaMapping(processing);
        }
    }
Call the DocumentProcessor of this call.

@param processing the Processing object to use
@return the progress of the DocumentProcessor that was called
docproc/src/main/java/com/yahoo/docproc/Call.java