RFR 8080640: Reduce copying when reading JAR/ZIP entries

[Staffan Friberg]

Hi,

Wanted to get reviews and feedback on this performance improvement for 
reading from JAR/ZIP files during classloading by reducing unnecessary 
copying and reading the entry in one go instead of in small portions. 
This shows a significant improvement when reading a single entry and for 
a large application with 10k classes and 500+ JAR files it improved the 
startup time by 4%.

For more details on the background and performance results please see 
the RFE entry.

RFE - https://bugs.openjdk.java.net/browse/JDK-8080640
WEBREV - http://cr.openjdk.java.net/~sfriberg/JDK-8080640/webrev.0

Cheers,
Staffan