Add a Clock and TickClock interface for mocking out time

sync/notifier/ack_tracker.h

 // Copyright (c) 2012 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 SYNC_NOTIFIER_ACK_TRACKER_H_
 #define SYNC_NOTIFIER_ACK_TRACKER_H_
 
 #include <map>
 
 #include "base/basictypes.h"
 #include "base/callback_forward.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/threading/thread_checker.h"
 #include "base/time.h"
 #include "base/timer.h"
 #include "net/base/backoff_entry.h"
 #include "sync/notifier/invalidation_util.h"
 
+namespace base {
+class TickClock;
+}  // namespace base
+
 namespace syncer {
 
 // A simple class that tracks sets of object IDs that have not yet been
 // acknowledged. Internally, it manages timeouts for the tracked object IDs and
 // periodically triggers a callback for each timeout period. The timeout is a
 // simple exponentially increasing time that starts at 60 seconds and is capped
 // at 600 seconds.
 class AckTracker {
  public:
   class Delegate {
    public:
     virtual ~Delegate();
 
     // |ids| contains all object IDs that have timed out in this time interval.
     virtual void OnTimeout(const ObjectIdSet& ids) = 0;
   };
 
-  typedef base::Callback<base::TimeTicks()> NowCallback;
   typedef base::Callback<scoped_ptr<net::BackoffEntry>(
       const net::BackoffEntry::Policy* const)> CreateBackoffEntryCallback;
 
-  explicit AckTracker(Delegate* delegate);
+  AckTracker(base::TickClock* tick_clock, Delegate* delegate);
   ~AckTracker();
 
   // Equivalent to calling Ack() on all currently registered object IDs.
   void Clear();
 
   // Starts tracking timeouts for |ids|. Timeouts will be triggered for each
   // object ID until it is acknowledged. Note that no de-duplication is
   // performed; calling Track() twice on the same set of ids will result in two
   // different timeouts being triggered for those ids.
   void Track(const ObjectIdSet& ids);
   // Marks a set of |ids| as acknowledged.
   void Ack(const ObjectIdSet& ids);
 
   // Testing methods.
-  void SetNowCallbackForTest(const NowCallback& now_callback);
   void SetCreateBackoffEntryCallbackForTest(
       const CreateBackoffEntryCallback& create_backoff_entry_callback);
   // Returns true iff there are no timeouts scheduled to occur before |now|.
   // Used in testing to make sure we don't have timeouts set to expire before
   // when they should.
   bool TriggerTimeoutAtForTest(base::TimeTicks now);
   bool IsQueueEmptyForTest() const;
   const base::Timer& GetTimerForTest() const;
 
  private:
   struct Entry {
     Entry(scoped_ptr<net::BackoffEntry> backoff, const ObjectIdSet& ids);
     ~Entry();
 
     scoped_ptr<net::BackoffEntry> backoff;
     ObjectIdSet ids;
 
    private:
     DISALLOW_COPY_AND_ASSIGN(Entry);
   };
 
   void NudgeTimer();
   void OnTimeout();
   void OnTimeoutAt(base::TimeTicks now);
 
   static scoped_ptr<net::BackoffEntry> DefaultCreateBackoffEntryStrategy(
       const net::BackoffEntry::Policy* const policy);
 
   // Used for testing purposes.
-  NowCallback now_callback_;
   CreateBackoffEntryCallback create_backoff_entry_callback_;
 
+  base::TickClock* const tick_clock_;
+
   Delegate* const delegate_;
 
   base::OneShotTimer<AckTracker> timer_;
   // The time that the timer should fire at. We use this to determine if we need
   // to start or update |timer_| in NudgeTimer(). We can't simply use
   // timer_.desired_run_time() for this purpose because it always uses
   // base::TimeTicks::Now() as a reference point when Timer::Start() is called,
   // while NudgeTimer() needs a fixed reference point to avoid unnecessarily
   // updating the timer.
   base::TimeTicks desired_run_time_;
   std::multimap<base::TimeTicks, Entry*> queue_;
 
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(AckTracker);
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_NOTIFIER_ACK_TRACKER_H_