Customer stress test crashes during heap inspection using PrintClassHistogram.

Crashes while testing 6.0_17-b02 and 1.5.0_22-b02.

Crashing in -Xint mode.

Unable to reproduce with CMS GC or with serial collector.

-XX:+VerifyBeforeGC, -XX:+VerifyDuringGC, and -XX:+VerifyAfterGC do not report a problem.

Example stack: pstack19441_xint.out

----------------- lwp# 18 / thread# 18 --------------------
...snip...
 --- called from signal handler with signal 11 (SIGSEGV) ---
 fe8ba6e4 bool KlassInfoTable::record_instance(oopDesc*const) (6c1ff8dc, dd80bf70, 6f8b60, e0237118, 0, dd80bf70) + 30
 fe8bb154 void RecordInstanceClosure::do_object(oopDesc*) (6c1ff8cc, dd80bf70, c00c0501, 6d400448, 48, 49) + 8
 fe65d16c void MutableSpace::object_iterate(ObjectClosure*) (33d08, 6c1ff8cc, 48, e0237118, fede4ed4, dd80bf70) + 24
 feb31fd4 void PSYoungGen::object_iterate(ObjectClosure*) (34540, 6c1ff8cc, 34408, d6a918, fe65d148, fedeb5c8) + 10
 feb0ab84 void ParallelScavengeHeap::object_iterate(ObjectClosure*) (feded800, 6c1ff8cc, 4e2b, feb0ab70, fededa18, feded800)
+ 14
 fe8baed8 void HeapInspection::heap_inspection(outputStream*) (2cfa0, 4e2b, 34408, d6a918, 0, fecbdde4) + 1fc
 fec0932c void VM_GC_HeapInspection::doit() (6beffc80, 4bc, 7f7b2f, fedec490, fee, 7f74c1) + 9c
 fe5d8088 void VM_Operation::evaluate() (6beffc80, 2de08, fedb2000, fee, 7f74c1, 3a400) + 80
 fec0bc30 void VMThread::evaluate_operation(VM_Operation*) (2de08, 6beffc80, 1c2750, 7f74c1, 1c2758, fedb2000) + cc
 fec0c1c8 void VMThread::loop() (0, 3d1a0, 2f708, 1, fee02dd0, 4a968) + 45c
 fe65a92c void VMThread::run() (1c2400, 39400, fedeb74c, fedb2000, 3974c, 39400) + 98
 feaf5910 java_start (1c2400, 4bf1, fedb2000, fed00079, 1c36d0, fedfb3f4) + 22c
 ff2c6d4c _lwp_start (0, 0, 0, 0, 0, 0)