[Offline Pages] Add expiration in internal log.

components/offline_pages/offline_page_model_impl.cc

Index: components/offline_pages/offline_page_model_impl.cc
diff --git a/components/offline_pages/offline_page_model_impl.cc b/components/offline_pages/offline_page_model_impl.cc
index f08f1feefb1e2accacc8d5f76395a994a43ffd2f..a4d63b2595aa929393db9452dd9373ae7f60891c 100644
--- a/components/offline_pages/offline_page_model_impl.cc
+++ b/components/offline_pages/offline_page_model_impl.cc
@@ -664,6 +664,7 @@ void OfflinePageModelImpl::OnExpirePageDone(int64_t offline_id,
   if (iter != offline_pages_.end()) {
     iter->second.expiration_time = expiration_time;
     ClientId client_id = iter->second.client_id;
+    offline_event_logger_.RecordPageExpired(std::to_string(offline_id));
     base::HistogramBase* histogram = base::Histogram::FactoryGet(
         AddHistogramSuffix(client_id, "OfflinePages.ExpirePage.PageLifetime"),
         1, base::TimeDelta::FromDays(30).InMinutes(), 50,