Add a failure expectation for an incoming WPT

No-Try because the test hasn't arrived yet.

TBR=lpz

No-Try: True
Bug: 994214
Change-Id: I522b21423261f1f9d3cdccad6c3a40edc78b9185
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1755973
Reviewed-by: Robert Ma <robertma@chromium.org>
Commit-Queue: Robert Ma <robertma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#687280}

third_party/blink/web_tests/TestExpectations

@@ -3241,6 +3241,9 @@ crbug.com/785230 external/wpt/css/css-text-decor/text-decoration-thickness-verti
 # Flaky because of timestamps in error messages.
 crbug.com/991295 external/wpt/web-animations/timing-model/timelines/document-timelines.html [ Pass Failure ]
 
+# Random string in the error message
+crbug.com/994214 external/wpt/html/cross-origin-opener-policy/coop-navigated-popup.https.html [ Failure ]
+
 # ====== New tests from wpt-importer added here ======
 crbug.com/626703 [ Linux ] external/wpt/css/css-ui/appearance-textfield-001.html [ Failure ]
 crbug.com/626703 [ Mac ] external/wpt/css/css-ui/appearance-textfield-001.html [ Failure ]