Flaky failure of corelib_2/list_get_range_test with --optimization-counter-threshold=5

[alexmarkov]

This test failed on vm-kernel-optcounter-threshold-linux-release-ia32 bot:

FAILED: dartk-vm release_ia32 corelib_2/list_get_range_test
Expected: Pass
Actual: RuntimeError

--- Command "vm" (took 04.000389s):
DART_CONFIGURATION=ReleaseIA32 out/ReleaseIA32/dart --optimization-counter-threshold=5 --sync-async --ignore-unrecognized-flags --packages=/b/s/w/ir/.packages /b/s/w/ir/tests/corelib_2/list_get_range_test.dart

exit code:
255

stderr:
Unhandled exception:
Concurrent modification during iteration: Instance of 'SubListIterable<int>'.
#0      ListIterator.moveNext (dart:_internal/iterable.dart:337:7)
#1      testGetRange (file:///b/s/w/ir/tests/corelib_2/list_get_range_test.dart:26:27)
#2      main (file:///b/s/w/ir/tests/corelib_2/list_get_range_test.dart:50:3)
#3      _startIsolate.<anonymous closure> (dart:isolate/runtime/libisolate_patch.dart:289:19)
#4      _RawReceivePortImpl._handleMessage (dart:isolate/runtime/libisolate_patch.dart:171:12)

--- Re-run this test:
python tools/test.py -n dartk-optcounter-linux-release-ia32 corelib_2/list_get_range_test

I was able to reproduce the failure using commands

tools/build.py -m release -a ia32 runtime
tools/test.py --repeat 1000 -n dartk-optcounter-linux-release-ia32 corelib_2/list_get_range_test

It failed only once per 1000 runs.

[alexmarkov]

Both corelib_2/list_get_range_test and corelib/list_get_range_test are currently passing (and not flaky) on all configurations.