[8u] RFR(S) 8044107 : Add Diagnostic Command to list all ClassLoaders

[David Buck]

Hi!

Please review this very simple serviceability backport to 8u. The only 
difference between the JDK 9 changeset and the JDK 8 changeset is that 
the ClassLoaderDataGraph::cld_do function was already backported to JDK 
8 in the fix for 8049421 [0]. So the changes for adding 
classLoaderData.hpp|cpp are already in JDK 8 line-for-line exactly the 
same as they are in JDK 9.

bug report:
https://bugs.openjdk.java.net/browse/JDK-8044107

JDK 9 changeset:
http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/56a35b09e0d4

JDK 9 code review thread
May 2014: 
http://mail.openjdk.java.net/pipermail/hotspot-dev/2014-May/014072.html
June 2014: 
http://mail.openjdk.java.net/pipermail/hotspot-dev/2014-June/014127.html

JDK 8 webrev for review:
http://cr.openjdk.java.net/~dbuck/8044107_jdk8_ver00/

Testing:
JPRT (hotspot testset)
jtreg test included in changeset
manually confirmed new diagnostic command works as expected

Cheers,
-Buck

[0] http://hg.openjdk.java.net/jdk8u/jdk8u/hotspot/rev/2c6ef90f030a