The test became flaky somewhere between [r252676-r252827]: * http/tests/cache/disk-cache/speculative-validation/validation-request.html [r252676-r252816] UNKNOWN r252817 NOERROR [r252818-r252826] UNKNOWN r252827 TEXT (Expected: PASS) Within that range, r252778 (Speculative loading sometimes happens too early and is missing login cookies) seems the likely cause, since it was the only revision that modified the test.
Fixed by r259712.