Comment 4 for bug 1858500

Verified working. I followed the steps in the test case: in a clean disco VM, I installed chromium-browser (and verified that the chromium snap wasn't installed). I then dist-upgraded the VM to eoan, and verified that chromium-browser hadn't been updated, and that the chromium snap still wasn't there. I then enabled eoan-proposed in /etc/apt/source.list, updated, installed the chromium-browser update that was available (79.0.3945.79-0ubuntu0.19.10.2), and the chromium snap got installed, as expected.