RFR: Pauses that do not affect heap occupancy should not report heap

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/stats-no-pause-heap/webrev.02/

We have done this before for Init Mark. After async region recycling, Final Mark and Final Update
Refs are not freeing up the heap themselves. Ditto for Init and Final Partial GC.

Sample cycles:

[19.879s][info][gc] GC(5) Pause Init Partial 2.188ms
[19.889s][info][gc] GC(5) Concurrent partial GC 21740M->21828M(102400M) 10.035ms
[19.890s][info][gc] GC(5) Pause Final Partial 1.028ms
[19.894s][info][gc] GC(5) Concurrent cleanup 21828M->1312M(102400M) 4.296ms

...and:

[121.084s][info][gc] GC(9) Pause Init Mark 0.776ms
[121.317s][info][gc] GC(9) Concurrent marking 81944M->83220M(102400M) 232.421ms
[121.320s][info][gc] GC(9) Concurrent precleaning 83220M->83236M(102400M) 3.476ms
[121.356s][info][gc] GC(9) Pause Final Mark 35.520ms
[121.356s][info][gc] GC(9) Concurrent cleanup 83264M->21162M(102400M) 0.305ms
[121.441s][info][gc] GC(9) Concurrent evacuation  21162M->22165M(102400M) 84.215ms
[121.441s][info][gc] GC(9) Pause Init Update Refs 0.050ms
[121.698s][info][gc] GC(9) Concurrent update references  22169M->23389M(102400M) 256.810ms
[121.699s][info][gc] GC(9) Pause Final Update Refs 0.522ms
[121.700s][info][gc] GC(9) Concurrent cleanup 23389M->4630M(102400M) 0.859ms

Testing: hotspot_gc_shenandoah

Thanks,
-Aleksey