Jenkins sporadically reports failures of the mediawiki-extensions-hhvm job on innocuous, newly-rebased changes in mediawiki/core. For example https://integration.wikimedia.org/ci/job/mediawiki-extensions-hhvm/5936/consoleFull
```
There were 7 errors:
1) ApiFlowThankTest::testRequestWithoutToken
RuntimeException: Cannot override frozen service "storage".
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/extensions/Flow/vendor/Pimple/Container.php:76
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/extensions/Thanks/tests/ApiFlowThankIntegrationTest.php:93
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/tests/phpunit/MediaWikiTestCase.php:132
2) ApiFlowThankTest::testInvalidRequest
RuntimeException: Cannot override frozen service "storage".
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/extensions/Flow/vendor/Pimple/Container.php:76
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/extensions/Thanks/tests/ApiFlowThankIntegrationTest.php:93
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/tests/phpunit/MediaWikiTestCase.php:132
3) ApiFlowThankTest::testValidRequest
RuntimeException: Cannot override frozen service "storage".
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/extensions/Flow/vendor/Pimple/Container.php:76
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/extensions/Thanks/tests/ApiFlowThankIntegrationTest.php:93
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/tests/phpunit/MediaWikiTestCase.php:132
4) ApiFlowThankTest::testRequestWithInvalidId
RuntimeException: Cannot override frozen service "storage".
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/extensions/Flow/vendor/Pimple/Container.php:76
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/extensions/Thanks/tests/ApiFlowThankIntegrationTest.php:93
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/tests/phpunit/MediaWikiTestCase.php:132
5) ApiFlowThankTest::testRequestWithOwnId
RuntimeException: Cannot override frozen service "storage".
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/extensions/Flow/vendor/Pimple/Container.php:76
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/extensions/Thanks/tests/ApiFlowThankIntegrationTest.php:93
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/tests/phpunit/MediaWikiTestCase.php:132
6) ApiFlowThankTest::testApiTestGroup
RuntimeException: Cannot override frozen service "storage".
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/extensions/Flow/vendor/Pimple/Container.php:76
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/extensions/Thanks/tests/ApiFlowThankIntegrationTest.php:93
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/tests/phpunit/MediaWikiTestCase.php:132
7) ApiFlowThankTest::testMediaWikiTestCaseParentSetupCalled
RuntimeException: Cannot override frozen service "storage".
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/extensions/Flow/vendor/Pimple/Container.php:76
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/extensions/Thanks/tests/ApiFlowThankIntegrationTest.php:93
/mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/tests/phpunit/MediaWikiTestCase.php:132
```
I'm not sure exactly when it started, but at least as early as [[https://integration.wikimedia.org/ci/job/mediawiki-extensions-hhvm/5894/|build #5894]]. The [[https://integration.wikimedia.org/ci/job/mediawiki-extensions-hhvm/test/?width=800&height=600&failureOnly=true|failure rate graph]] shows a spike at around that time. https://gerrit.wikimedia.org/r/#/c/192608/ is presumably implicated, but perhaps was merged too early to be the whole story.