RFR 8202578: Revisit location for class unload events

[Harold David Seigel]

Hi,

Please review this fix for JDK-8202578.  The fix enables posting of JFR 
class unloading events without requiring a separate JFR-specific 
iteration through the class loader data graph.

Open Webrev: 
http://cr.openjdk.java.net/~hseigel/bug_8202578/webrev/index.html

JBS Bug:  https://bugs.openjdk.java.net/browse/JDK-8202578

This fix was regression tested by running Mach5 tiers 1 and 2 tests and 
builds on Linux-x64, Windows, and Mac OS X, running tiers 3-5 tests on 
Linux-x64, and by running JCK-11 Lang and VM tests on Linux-x64. 
Additionally, the jdk JFR tests were run explicitly.

Thanks, Harold