Update: Better answer: https://android.stackexchange.com/a/232571/121619
I couldn't find a good solution, but here's what I did, and it was really irritating I had to do this, but it worked:
Solution: Uninstall the Chrome app, then reinstall it:
- First, go to here in Chrome on your computer (
chrome://history/syncedTabs) and open up on your computer any tabs (that you see open on your phone device) that you'd like to send back to your phone later to essentially "keep open".
- From your phone: Uninstall the Chrome app from your phone: Play Store --> click 3 horizontal bars in top-left (sometimes called the "hamburger icon") --> "My Games and Applications" ("Mes jeux et applications" in French) --> "Installed Applications" ("Applications installées") tab --> scroll down to Chrome and tap on it --> click the "Uninstall" ("Désinstaller") button.
- When done, reinstall it. This seems to have worked. All tabs are now closed in Chrome, and it shows I have
1 tab open!
- From your computer: "Restore" the few tabs you wanted to keep open by simply right-clicking the tabs on your computer you wanted to send back to your phone, and selecting "Send to your devices" --> "Google phone". On your phone, a notification will pop up. Click it to open the new tab in Chrome. You have to do this once per tab you'd like back open on your phone. I did this for about 10 of my 494 tabs I had open on my phone. So, now I'm back to 10 open tabs on my phone.
How dumb I had to uninstall the entire app to close all the tabs at once.
GOOGLE/CHROME, PLEASE FIX THIS! MANY THANKS IN ADVANCE! Update: do this instead. See the comments under that answer too (nevermind, an admin deleted them--just be sure to click the number of open tabs icon BEFORE clicking the 3 dots icon is all, as doing that step first causes the 3 dots menu to change).
Note that prior to uninstalling the Chrome app on the phone I also cleared all of its cache and storage data on the phone. This did NOT close all the tabs by itself. The complete "Uninstall" process was required. I'm not sure if doing these two things prior to uninstalling the app had any effect on the uninstall/reinstall process, but in case it did, I'm mentioning it here. I don't think it did.