components: Cleanup class/struct fwd declarations

components/sync/engine_impl/cycle/data_type_debug_info_emitter.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 COMPONENTS_SYNC_ENGINE_IMPL_CYCLE_DATA_TYPE_DEBUG_INFO_EMITTER_H_
 #define COMPONENTS_SYNC_ENGINE_IMPL_CYCLE_DATA_TYPE_DEBUG_INFO_EMITTER_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "base/observer_list.h"
 #include "components/sync/base/model_type.h"
 #include "components/sync/engine/cycle/commit_counters.h"
 #include "components/sync/engine/cycle/update_counters.h"
 
 namespace syncer {
 
-class DirectoryCommitContributor;
 class TypeDebugInfoObserver;
 
 // Supports various kinds of debugging requests for a certain directory type.
 //
 // The Emit*() functions send updates to registered TypeDebugInfoObservers.
 // The DataTypeDebugInfoEmitter does not directly own that list; it is
 // managed by the ModelTypeRegistry.
 //
 // For Update and Commit counters, the job of keeping the counters up to date
 // is delegated to the UpdateHandler and CommitContributors. For the Stats
@@ skipping 42 matching lines @@
  private:
   CommitCounters commit_counters_;
   UpdateCounters update_counters_;
 
   DISALLOW_COPY_AND_ASSIGN(DataTypeDebugInfoEmitter);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_ENGINE_IMPL_CYCLE_DATA_TYPE_DEBUG_INFO_EMITTER_H_