We should add histogram to record how many requests were successfully fetched via different data reduction proxies. e.g., how many requests were successfully fetched via primary proxy, secondary proxy etc. This would help in multiple ways:
(i) Quantifying if using QUIC has any effect on how frequently primary proxy is used.
(ii) Detecting any regression in use of primary proxy.
(iii) Once the flywheel config server starts sending more than 2 proxies in the configuration, it will be useful to see how frequently the third proxy is used, and if that fallback mechanism is working correctly or not.