Mark external/wpt/lifecycle/freeze.html as flaky.

TBR=dtapuska@chromium.org

Bug: 1020036
Change-Id: I5add7fa7b57e7ace63e84599ca3b120a71a933a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1890463Reviewed-by: Alice Boxhall <aboxhall@chromium.org>
Commit-Queue: Alice Boxhall <aboxhall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#711147}

third_party/blink/web_tests/TestExpectations

@@ -5772,4 +5772,5 @@ crbug.com/940927 external/wpt/trusted-types/trusted-types-eval-reporting-no-unsa
 crbug.com/940927 external/wpt/trusted-types/eval-with-permissive-csp.tentative.html [ Failure ]
 
 # Sheriff 2019-10-31
-crbug.com/1020034 [ Mac10.10 ] fast/forms/month/month-appearance-l10n.html [ Failure ]
+crbug.com/1020034 [ Mac10.10 ] fast/forms/month/month-appearance-l10n.html [ Failure ]
\ No newline at end of file
+crbug.com/1020036 [ Debug ] external/wpt/lifecycle/freeze.html [ Failure Pass ]