RFR (JDK 13/java.xml) 8223658: Performance regression of XML.validation in 13-b19

[Joe Wang]

Please review a fix to the performance regression introduced by Xerces 
update. The performance benchmark gives weight to small XML files. Large 
chunk sizes are therefore not helpful. Performance tests with the 
following patch showed that the results are on par with that for JDK 13 b18.

https://bugs.openjdk.java.net/browse/JDK-8223658
http://cr.openjdk.java.net/~joehw/jdk13/8223658/webrev/

Thanks,
Joe