Implement new invalidations ack tracking system

sync/sessions/nudge_tracker.h

 // Copyright 2013 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.
 //
 // A class to track the outstanding work required to bring the client back into
 // sync with the server.
 #ifndef SYNC_SESSIONS_NUDGE_TRACKER_H_
 #define SYNC_SESSIONS_NUDGE_TRACKER_H_
 
 #include <list>
 #include <map>
 
 #include "base/compiler_specific.h"
 #include "sync/base/sync_export.h"
 #include "sync/internal_api/public/base/model_type.h"
-#include "sync/notifier/object_id_invalidation_map.h"
 #include "sync/protocol/sync.pb.h"
 #include "sync/sessions/data_type_tracker.h"
 
 namespace syncer {
+
+class ObjectIdInvalidationMap;
+
 namespace sessions {
 
 class SYNC_EXPORT_PRIVATE NudgeTracker {
  public:
   static size_t kDefaultMaxPayloadsPerType;
 
   NudgeTracker();
   ~NudgeTracker();
 
   // Returns true if there is a good reason for performing a sync cycle.
@@ skipping 97 matching lines @@
 
   size_t num_payloads_per_type_;
 
   DISALLOW_COPY_AND_ASSIGN(NudgeTracker);
 };
 
 }  // namespace sessions
 }  // namespace syncer
 
 #endif  // SYNC_SESSIONS_NUDGE_TRACKER_H_