@lizeb: One way to fix this would be to attach the CustomTabObserver as well as PageLoadMetricObserver to a hidden tab when it's created in CustomTabsConnection. If CustomTabActivity takes a hidden tab, it could avoid creating new observers in initializeMainTab. So that's all do-able, if a little messy.

A bigger question might be what to do with the notifications. Broadcasting metrics for prerendered tabs that are not explicitly navigated to will be a change from what CCT clients currently see and it may be difficult (or at least different from their current implementation) for them to distinguish prerendered events from a "real" page load. In other words, the usual prerendering problem.

An alternative might be to batch up the notifications that would be sent while the hidden tab loads, and send them only when the hidden tab is taken and shown. Since all the notifications are piped through CustomTabsConnection, this wouldn't be too hard, but would be a fair amount of work for something that's arguably not a big deal.

Do you have any opinion?

[delayed] update:

It has turned out in practice that this issue is not critical for network quality metrics. In view of the new policy on metrics exported to CCT [1], it does not seem worth doing much in this direction.

[1] https://docs.google.com/document/d/16ZBWOl06BTUKnRMjZDI0uFl9bXUZoymyz4KvOWN8I9g/edit