Only report ReadingList.OfflineVersionDisplayed for URL in Reading List.

ios/chrome/browser/reading_list/reading_list_web_state_observer.mm

Index: ios/chrome/browser/reading_list/reading_list_web_state_observer.mm
diff --git a/ios/chrome/browser/reading_list/reading_list_web_state_observer.mm b/ios/chrome/browser/reading_list/reading_list_web_state_observer.mm
index 0ca54adae018555d354449622a0646e3f43d9308..44e13b3569eb07ec64773dde4c8e9b14c76a8c44 100644
--- a/ios/chrome/browser/reading_list/reading_list_web_state_observer.mm
+++ b/ios/chrome/browser/reading_list/reading_list_web_state_observer.mm
@@ -208,7 +208,8 @@ void ReadingListWebStateObserver::PageLoaded(
   last_load_result_ = load_completion_status;
   web::NavigationItem* item =
       web_state()->GetNavigationManager()->GetLastCommittedItem();
-  if (!item || !pending_url_.is_valid()) {
+  if (!item || !pending_url_.is_valid() ||
+      !reading_list_model_->GetEntryByURL(pending_url_)) {
     StopCheckingProgress();
     return;
   }