How to know if Google Chrome has finished synchronizing?

You can type chrome://sync-internals in the omnibox. It lets you view internal and technical data about your connection to the Google Cloud. It is actually intended for developers, but it can also be used to know the status of the sync.

In the About tab, you can find "Last Synced", if it shows "Just Now" you can be sure that the sync process completed just now, and be sure that everything has been synced.
There is one more field "Sync Cycle Ongoing" which shows the status of sync, if its true it means the sync is being done and you should wait.

You can experiment with it by adding/removing a bookmark and observe the changes on the page, this way you will be able to better understand the status of the sync and information displayed at page.

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