RFR: Should return zero actual allocated size when allocation failed

[Zhengyu Gu]

Several of vmTestbase gc tests failed due to following assertion:

#  Internal Error 
(/home/zgu/workspace/shenandoah-jdk/src/hotspot/share/gc/shared/collectedHeap.cpp:407), 
pid=2985, tid=3045
#  assert(actual_tlab_size == 0) failed: Allocation failed, but actual 
size was updated. min: 256, desired: 257, actual: 257

cause we return requested size even when allocation failed.

http://cr.openjdk.java.net/~zgu/shenandoah/new_tlab_size/webrev.00/

Test:

tier1_gc_shenandoah and manual test of failed vmTestbase tests


Thanks,

-Zhengyu