[WPT Import] Unblock importer by adding test expectation

An incoming test, html/cross-origin-opener-policy/blob-popup.https.html,
has non-deterministic output on failure. Add a TestExpectations-level
expectation for it to make the importer pass.

Bug: 1042347
Change-Id: I71067863e6938edf05a193d1c605e46c60022cd7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2003438
Commit-Queue: Robert Ma <robertma@chromium.org>
Reviewed-by: Robert Ma <robertma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#732165}

third_party/blink/web_tests/TestExpectations

@@ -6392,3 +6392,7 @@ crbug.com/1006759 http/tests/devtools/console/argument-hints.js [ Pass Failure ]
 # Failing origin trial for css proeprties test
 crbug.com/1041993 http/tests/origin_trials/sample-api-script-added-after-css-declaration.html [ Failure ]
 virtual/omt-worker-fetch/http/tests/origin_trials/sample-api-script-added-after-css-declaration.html [ Failure ]
+
+# ecosystem-infra sheriff 2020-01-15
+# Has non-deterministic output on failure, so cannot match -expected.txt
+crbug.com/1042347 external/wpt/html/cross-origin-opener-policy/blob-popup.https.html [ Failure ]