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 "base/time/tick_clock.h"
+#include "base/time/time.h"
 #include "url/gurl.h"
 
 // An entry in the reading list. The URL is a unique identifier for an entry, as
 // such it should not be empty and is the only thing considered when comparing
 // entries.
 class ReadingListEntry {
  public:
   ReadingListEntry(const GURL& url, const std::string& title);
+  // The lifetime of |clock| must enclose lifetime of ReadingListEntry, the
+  // pointer can be null.
+  ReadingListEntry(const GURL& url,
+                   const std::string& title,
+                   base::TickClock* clock);
   ReadingListEntry(const ReadingListEntry& entry);
   ~ReadingListEntry();
 
   // Entries are created in WAITING state. At some point they will be PROCESSING
   // into one of the three state: PROCESSED, the only state a distilled URL
   // would be set, WILL_RETRY, similar to wait, but with exponential delays or
   // ERROR where the system will not retry at all.
   enum DistillationState { WAITING, PROCESSING, PROCESSED, WILL_RETRY, ERROR };
 
   // 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;
+  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 time before the next try. This is automatically increased when the
+  // state is set to WILL_RETRY or ERROR.
+  base::TimeDelta TimeUntilNextTry() 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:
+  // Calculates the delta until the next retry based of the
+  // |currentWaitingTime|. This implementation doubles it.
+  static base::TimeDelta NextWaitingTime(base::TimeDelta currentWaitingTime);
+  // Get the current time using the clock or base::TimeTicks::Now() if no clock
+  // is provided.
+  base::TimeTicks GetTimeTicksNow() const;
+
   GURL url_;
   std::string title_;
   GURL distilled_url_;
   DistillationState distilled_state_;
+  base::TimeTicks time_to_retry_;
+  base::TimeDelta current_waiting_time_;
+  base::TickClock* clock_;
 };
 
 #endif  // IOS_CHROME_BROWSER_READING_LIST_READING_LIST_ENTRY_H_