Findit identified the culprit r550759 with confidence 100.0% in the config "chromium.chromiumos / linux-chromeos-rel"
based on the flakiness trend:

https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVypwELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCJxY2hyb21pdW0uY2hyb21pdW1vcy9saW51eC1jaHJvbWVvcy1yZWwvNjkwMi9pbnRlcmFjdGl2ZV91aV90ZXN0cy9RV3hzTDBGMWRHOW1hV3hzVTJsdVoyeGxRMnhwWTJ0VVpYTjBMa05zYVdOckx6ST0MCxITTWFzdGVyRmxha2VBbmFseXNpcxgBDA


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Hi Tommy.

Can you take a look at this?

The test that is flaky uses the following combination:
 - AutofillExpandedPopupViews: enabled
 - AutofillSingleClick: disabled

This is a sample run: https://chromium-swarm.appspot.com/task?id=3cdad9f8ccd23910&refresh=10&show_raw=1

It hangs on SendKeyToPopupAndWait(), but I'm not sure which one in AutofillSingleClickTest.Click this is (there is one for ARROW_DOWN and one for ENTER).

For the moment, I wouldn't like to revert the CL, because it brings better test coverage overall.

Sample run for future reference: https://chromium-swarm.appspot.com/task?id=3cdacce485258510&refresh=10&show_raw=1

I sent a revert to the CQ: https://chromium-review.googlesource.com/c/chromium/src/+/1014141

However, it's very concerning that we have so many disabled tests on ChromeOS for the same reason: a test hangs during SendKeyToPopupAndWait() only on ChromeOS. We should try to find an explanation for that and reenable all tests that in the same file.