RFR: JDK-8215026: Incorrect amount of memory unmapped with ImageFileReader::close()

[Jini George]

Hello,

This is a request to review the proposed change to fix:
https://bugs.openjdk.java.net/browse/JDK-8215026

The webrev is at:

http://cr.openjdk.java.net/~jgeorge/8215026/webrev.00/index.html

The background mail thread for this change is at: 
http://mail.openjdk.java.net/pipermail/jigsaw-dev/2018-December/014043.html

Thank you,
Jini.