On chrome://interstitials, the bad clock and SSL interstitials show the Extended Reporting checkbox, but the captive portal interstitial doesn't. That's because interstitials_ui sets a null |cert_report_helper|, and the captive portal interstitial (and only the captive portal interstitial) does not populate the extended reporting option if the |cert_report_helper| is null: https://cs.chromium.org/chromium/src/chrome/browser/ssl/captive_portal_blocking_page.cc?sq=package:chromium&rcl=1472642334&l=182