Currently, if a user turns off the data saver, their HTTP traffic is not proxied, and they do not receive any compression benefits. However, the data saver prefs that record the daily content lengths (original and compressed) are still incremented for every HTTP request. So, if the user turns on data saver in future at some point, they will have a large number of original and compressed bytes, but very little savings. This can cause confusion if the user visits the data saver settings page to look at the savings.

To see how frequently this happens, we should record the number of days since data saver is ON in UMA. This will also help in debugging some of the user feedback reports (e.g., low savings in https://bugs.chromium.org/p/chromium/issues/detail?id=571470#c25 could be because of user turning off data saver at some point in the past).