RFR (S): 8133530: Add JFR event for evacuation statistics

[Thomas Schatzl]

Hi,

On Fri, 2015-08-14 at 09:41 -0700, Staffan Friberg wrote:
> Hi Thomas,
> 
> Any reason to go via the G1EvacSummary class and not just send the stats 
> (G1EvacStats) straight through to the event code?
> 
> It seems like it just adds a very short live object and a lot of copies 
> of different fields, but I might miss some bigger picture thing.

  other similar code that wants to send more than a few variables in a
given event also introduces this kind of summary classes. The intention
is to decouple the gc_tracer a little from the collector
implementations.

I am not sure if it is the best way to do this, but it would somewhat
break the "style" of the other code. So for now I would like to keep the
code as is; I talked with others offline without real conclusion except
that it is probably best to implement the event dispatching uniformly at
this time.

The latest revision of the change does away a little with some more code
duplication too.

Thanks,
  Thomas