Add a TimeUntilNextTry to reading list

ios/chrome/browser/reading_list/reading_list_entry.h

Index: ios/chrome/browser/reading_list/reading_list_entry.h
diff --git a/ios/chrome/browser/reading_list/reading_list_entry.h b/ios/chrome/browser/reading_list/reading_list_entry.h
index 4201a0a9146a0ab77c8b66b8a70b47abde29847b..e17b3f39d1b2415c003726e5a9493e2b732bfae4 100644
--- a/ios/chrome/browser/reading_list/reading_list_entry.h
+++ b/ios/chrome/browser/reading_list/reading_list_entry.h
@@ -33,6 +33,11 @@ class ReadingListEntry {
   // The local file URL for the distilled version of the page. This should only
   // be called if the state is "PROCESSED".
   const GURL& DistilledURL() const;
+  // The number of times this entry has failed to download the distilled version
+  // of the page since its creation or the last PROCESSED state.
+  // This counter is automatically increased when the state is set to WILL_RETRY
+  // or ERROR.
+  int FailedDistillationCounter() const;
 
   ReadingListEntry& operator=(const ReadingListEntry& other);
   bool operator==(const ReadingListEntry& other) const;
@@ -49,6 +54,7 @@ class ReadingListEntry {
   std::string title_;
   GURL distilled_url_;
   DistillationState distilled_state_;
+  int failed_distillation_counter_;
 };
 
 #endif  // IOS_CHROME_BROWSER_READING_LIST_READING_LIST_ENTRY_H_