Appears to have been flaky for a while now (before PST sheriff checked in). Haven't been able to track down the offending patch.

https://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_rel_ng?numbuilds=200

example:
https://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_rel_ng/builds/450264

THE FOLLOWING ARE EXAMPLES OF FLAKY FAILURES:
Unexpected Failures:
* external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/variables/variable-declaration-18.html
* http/tests/misc/non-utf8-header-name.php
* http/tests/security/contentSecurityPolicy/directive-parsing-03.html
* http/tests/security/contentSecurityPolicy/source-list-parsing-04.html
* inspector/sources/debugger/rethrow-error-from-bindings-crash.html
* virtual/mojo-loading/http/tests/inspector/network/network-filters.html
* virtual/mojo-loading/http/tests/security/contentSecurityPolicy/directive-parsing-03.html
* virtual/mojo-loading/http/tests/security/contentSecurityPolicy/source-list-parsing-04.html
* virtual/mojo-loading/http/tests/security/document-domain-canonicalizes.html