RFR: 8015683: object_count_after_gc should have the same timestamp for all events

[Erik Helin]

Hi all,

this a "forward port" of the corresponding change in hotspot 24. The
patch from hotspot 24 did not apply cleanly for the following reasons:

- hotspot 24 has some classes that we do not want to expose since the
  are implementation details because of permgen. Hotspot 24 therefore
  uses an "ObjectCountFilter" that is not necessary in hotspot 25 since
  permgen has been replaced by metaspace.

- #ifndef SERIALGC has been replaced by #if INCLUDE_ALL_GCS in hotspot
  25.

- hotspot 25 can be compiled without some services such as heap
  inspection by using #if INCLUDE_SERVICES.

Please note that these differences are not important for the patch, they
only affect the surroundings of the changed lines.

Webrev: http://cr.openjdk.java.net/~ehelin/8015683/webrev.00/

Thanks,
Erik