This is similar to Issue 880655. It seems that we are not sending the pingback on cached responses.

I manually browsed many pages with my patch ((https://chromium-review.googlesource.com/c/chromium/src/+/1375459)) that checks if the pingback is sent on cached responses, however, I could not get it to trigger even though in many cases DevTools showed that the main frame response is being served from cache.

That patch also passed the CQ which seems highly suspicious since DataReductionProxyNetworkDelegate::OnHeadersReceivedInternal() is called for every URL request regardless of whether data saver is enabled or not.
 

This is similar to  Issue 880655 . It seems that we are not sending the pingback on cached responses.

I manually browsed many pages with my patch (https://chromium-review.googlesource.com/c/chromium/src/+/1375459) that checks if the pingback is sent on cached responses, however, I could not get it to trigger even though in many cases DevTools showed that the main frame response is being served from cache.

That patch also passed the CQ which seems highly suspicious since DataReductionProxyNetworkDelegate::OnHeadersReceivedInternal() is called for every URL request regardless of whether data saver is enabled or not.