RFR: 8015972: Refactor the sending of the object count after GC event

[Erik Helin]

Hi all,

this change is a "forward port" of the same change that was applied to
hotspot 24.

The difference between between the hotspot 24 version and the hotspot 25
version is that the INCLUDE_SERVICES define was added, and heap
inspection is part of INCLUDE_SERVICES. I have therefore included
ObjectCountEventSender under the INCLUDE_SERVICES define as well, since
it is completely dependent on the heap inspection functionality.

Webrev:
http://cr.openjdk.java.net/~ehelin/8015972/webrev.00/

Testing:
- JPRT

Thanks,
Erik