We should also add a test for this, automatic if possible but manual otherwise. 

This would be the steps to be tested for:
1) Launch Chrome and download an offline page.
2) Open the Downloads Home.
3) Open the downloaded offline page.
4) Hit Android's back button.
5) The Downloads Home should be brought back to the foreground.

Re #1: CC-ing test team members for awareness of the need for these tests.

While finishing bisecting over recently released Canary builds I figured out I cannot reproduce anymore. :/

Lowering priority and I will close it after a few more checks.

A teammate was able to repro it as well in their personal device on the same Canary version. I was able to repro it also on my personal device on Dev 71.0.3578.12. But getting data out of personal devices is difficult.

Anyway, given that on my test device the issue stopped once I had to reset Canary data when downgrading it for the bisect, it seems the problem is obvisouly based on persisted data state.

I think it has something to do with the CCT launch configuration. A small -- but maybe pertinent -- distinction I noticed is that the transition animation when launching and leaving the CCT is different between Chrome installations where this bug happens and doesn't.

For the installs where the bug happens, the CCT launch animation makes it come from the right side of the screen, sliding to the left while pushing the DH out of the screen. When hitting back the CCT animates "drops" it out of the screen to the right and down.

For the installs where it doesn't happen, the CCT animation makes the new window slide up from the bottom and hitting back makes it drop down back where it came from.

This seems to be consistent with other people's installs that shown/don't show this bug.

Finally I think this is just the Finch experiment doing its thing, setting 50% of the Canary/Dev/Beta population to have OP-in-CCT disabled. I hadn't realized initially that the cases where it doesn't go back to the DH are in fact not opening pages in CCTs but in regular new tabs (hence the animation difference).

So, nothing to see here, move along...