Test failure on vm/dart/isolates/concurrency_stress_sanity_test

[jyameo]

There are new test failures on Reformat tests/language/abstract..

The tests

vm/dart/isolates/concurrency_stress_sanity_test RuntimeError (expected Pass)

are failing on configurations

vm-appjit-linux-release-x64
vm-linux-release-x64

LOGS:
https://dart-ci.appspot.com/log/vm-appjit-linux-release-x64/vm-appjit-linux-release-x64/4736/vm/dart/isolates/concurrency_stress_sanity_test
https://dart-ci.appspot.com/log/vm-linux-release-x64/vm-linux-release-x64/4503/vm/dart/isolates/concurrency_stress_sanity_test

[dart-github-bot]

Summary: Concurrency stress sanity test fails on Linux x64 release builds (both appjit and non-appjit). Recent code changes are suspected.