RFR (M): 8008920: Tracing events for heap statistics

[Erik Helin]

Hi all,

this change adds an event, vm/gc/detailed/class_count_after_gc, that 
sends information about the number of instances of each class on the 
heap (as well as size and the name of the class).

The event is sent after the marking phase for all old collections and an 
object will be counted as live if the GC think that the object is live 
(this is only tricky in the case of a concurrent collection).

Webrev:
http://cr.openjdk.java.net/~ehelin/8008920/webrev.00/

Bug:
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8008920

Testing:
JPRT

Thanks,
Erik