components: Cleanup class/struct fwd declarations

components/sync/engine_impl/cycle/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.
 
 #ifndef COMPONENTS_SYNC_ENGINE_IMPL_CYCLE_NUDGE_TRACKER_H_
 #define COMPONENTS_SYNC_ENGINE_IMPL_CYCLE_NUDGE_TRACKER_H_
 
 #include <stddef.h>
 
 #include <list>
 #include <map>
 #include <memory>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/time/time.h"
 #include "components/sync/base/invalidation_interface.h"
 #include "components/sync/base/model_type.h"
 #include "components/sync/engine_impl/cycle/data_type_tracker.h"
 #include "components/sync/protocol/sync.pb.h"
 
 namespace syncer {
 
-class ObjectIdInvalidationMap;
-
 // A class to track the outstanding work required to bring the client back into
 // sync with the server.
 class NudgeTracker {
  public:
   static size_t kDefaultMaxPayloadsPerType;
 
   NudgeTracker();
   ~NudgeTracker();
 
   // Returns true if there is a good reason for performing a sync cycle.
@@ skipping 173 matching lines @@
   base::TimeDelta minimum_local_nudge_delay_;
   base::TimeDelta local_refresh_nudge_delay_;
   base::TimeDelta remote_invalidation_nudge_delay_;
 
   DISALLOW_COPY_AND_ASSIGN(NudgeTracker);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_ENGINE_IMPL_CYCLE_NUDGE_TRACKER_H_