RFR (S): 8066566: Refactor ParNewGeneration to contain ParNewTracer

[Marcus Larsson]

Hi,

I would like reviews for the following small patch.

Like the bug description says, the ParNewTracer is stack-allocated 
during ParNewGeneration::collect(), forcing us to send the tracer as an 
argument to functions that might need it. This patch moves the tracer, 
and makes it a field in ParNewGeneration instead.

The change includes adding a getter for this field, even though it is 
not used, however, future changes adding PLAB tracing [1] will require this.

Webrev:
http://cr.openjdk.java.net/~mlarsson/8066566/webrev.00/

Bug:
https://bugs.openjdk.java.net/browse/JDK-8066566

Testing:
jprt

Thanks,
Marcus

[1]: https://bugs.openjdk.java.net/browse/JDK-8055845