Do you see this on Beta as well?

Which device you are able repro this? I build from trunk and i didn't see the issue.

Could it be that the text are in white color so you won't be able to see it? 
But wrong text color is also very strange.

On beta (54.0.2480.50) I do see the text. And there it warns on both .apk and .spl, even though my change to download_file_types.asciipb to additionally warn on apks is not in beta.  So this is confusing to me.

For beta, the finch experiment of disabling android DownloadManager is 50%

So you have 50% of the chance that are still using android DM, and that code path checks .apk

I was testing on my personal Nexus 5x, and I got the Canary build from the google.com part of playstore. https://play.google.com/store/apps/details?id=com.chrome.canary

The blank warning still repros on the latest canary, 56.0.2886.0.  It doesn't repro on dev or beta for me, but I'm unsure of my experiment state.

Varun can also repro the blank warning on the same canary, on N5x.

qinmin -- Can you repro this? 

Yes, I can repro.
The java implementation of the dangerous infobar should be deprecated, i am rewriting that.

Sorry, wrong bug, I cannot repro this one.

met with Varun, and we cannot repro the problem on his device, with both incognito and non-incognito mode.

OK, I can no longer repro on 56.0.2889.0, so I'm assuming it was fixed between .2886.0 and .2889.0.