Add a TimeUntilNextTry to reading list

ios/chrome/browser/reading_list/reading_list_entry.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef IOS_CHROME_BROWSER_READING_LIST_READING_LIST_ENTRY_H_
 #define IOS_CHROME_BROWSER_READING_LIST_READING_LIST_ENTRY_H_
 
 #include <string>
 
 #include "url/gurl.h"
@@ skipping 15 matching lines @@
 
   // The URL of the page the user would like to read later.
   const GURL& URL() const;
   // The title of the entry. Might be empty.
   const std::string Title() const;
   // What state this entry is in.
   DistillationState DistilledState() const;
   // 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;
 
   // Sets the title.
   void SetTitle(const std::string& title);
   // Sets the distilled URL and switch the state to PROCESSED.
   void SetDistilledURL(const GURL& url);
   // Sets the state to one of PROCESSING, WILL_RETRY or ERROR.
   void SetDistilledState(DistillationState distilled_state);
 
  private:
   GURL url_;
   std::string title_;
   GURL distilled_url_;
   DistillationState distilled_state_;
+  int failed_distillation_counter_;
 };
 
 #endif  // IOS_CHROME_BROWSER_READING_LIST_READING_LIST_ENTRY_H_