RFR: JDK-8055845 - Add trace event for promoted objects

[Staffan Friberg]

Hi,

Could I please get reviews for this RFE that adds a trace event for 
aging and promotion for young collections in G1, CMS and Parallel GC.
It works similarly to allocation events, and generates the event on the 
slow path when either a direct copy occurs or a new PLAB is request.

Since I'm adding an event I cc:ed the serviceability list in case anyone 
has any comments on the event and changes to trace.xml.

RFE: https://bugs.openjdk.java.net/browse/JDK-8055845
Webrev: http://cr.openjdk.java.net/~brutisso/8055845/webrev.00

Bengt has been kind and agreed to both sponsor and host the the webrev.

Thanks,
Staffan