Flaky crash in vm/dart_2/trigger_gc_in_native_test/1

[mkustermann]

From log:

/============================================================================\
| vm/dart_2/trigger_gc_in_native_test/1 broke (Pass -> Crash, expected Pass) |
\============================================================================/

--- Command "vm" (took 08.000167s):
DART_CONFIGURATION=DebugX64 out/DebugX64/dart --hot-reload-rollback-test-mode --no_concurrent_mark --concurrent_sweep --ignore-unrecognized-flags --packages=/b/s/w/ir/.packages /b/s/w/ir/runtime/tests/vm/dart_2/trigger_gc_in_native_test.dart

exit code:
-6

stderr:
../../runtime/vm/raw_object.cc: 245: error: expected: use_saved_class_table || class_table->SizeAt(class_id) > 0
version=2.10.0-edge.ca743398c2145c8147f5e6cbaba1416d8643b66e (be) (Thu Jul 30 06:21:20 2020 +0000) on "linux_x64"
pid=16829, thread=16844, isolate_group=main(0x55d92bb48580), isolate=(nil)((nil))
isolate_instructions=55d9298307a0, vm_instructions=55d9298307a0
  pc 0x000055d929c21a2c fp 0x00007fdf0befea60 dart::Profiler::DumpStackTrace(void*)+0x7c
  pc 0x000055d9298308d2 fp 0x00007fdf0befeb40 dart::Assert::Fail(char const*, ...)+0x82
  pc 0x000055d929c3ddb6 fp 0x00007fdf0befeb90 dart::ObjectLayout::HeapSizeFromClass(unsigned int) const+0x716
  pc 0x000055d929d3cbdf fp 0x00007fdf0befec00 dart::GCSweeper::SweepPage(dart::OldPage*, dart::FreeList*, bool)+0xef
  pc 0x000055d929d3d8b0 fp 0x00007fdf0befec90 out/DebugX64/dart+0x1f798b0
  pc 0x000055d929ce870b fp 0x00007fdf0befed30 dart::ThreadPool::WorkerLoop(dart::ThreadPool::Worker*)+0x1cb
  pc 0x000055d929ce9149 fp 0x00007fdf0befed80 dart::ThreadPool::Worker::Main(unsigned long)+0x179
  pc 0x000055d929c1a9d9 fp 0x00007fdf0befeed0 out/DebugX64/dart+0x1e569d9
-- End of DumpStackTrace

--- Re-run this test:
python tools/test.py -n dartk-reload-rollback-linux-debug-x64 vm/dart_2/trigger_gc_in_native_test/1

/cc @rmacnak-google