Chrome Complains that I Need to Enter Sync Passphrase (But I've Forgotten It)

If you no longer have access to your custom passphrase, you’ll need to reset sync:

1. If your synced data (bookmarks, apps, etc) is available on your local computer, sign in to your Google Dashboard. (There will often be a link on the box)
2. In the Chrome Sync section, click Stop sync and delete data from Google. This step will remove the data from Google’s servers. The data on your local computer won’t be affected.
3. Wait a few minutes before signing in to Chrome and re-enabling sync on your computer.

(link to google product forms)