components: Cleanup class/struct fwd declarations

components/sync/model_impl/shared_model_type_processor.h

 // Copyright 2014 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_MODEL_IMPL_SHARED_MODEL_TYPE_PROCESSOR_H_
 #define COMPONENTS_SYNC_MODEL_IMPL_SHARED_MODEL_TYPE_PROCESSOR_H_
 
 #include <map>
 #include <memory>
 #include <string>
 #include <unordered_set>
 
 #include "base/memory/weak_ptr.h"
 #include "base/threading/non_thread_safe.h"
 #include "components/sync/base/model_type.h"
 #include "components/sync/engine/cycle/status_counters.h"
 #include "components/sync/engine/model_type_processor.h"
 #include "components/sync/engine/non_blocking_sync_common.h"
 #include "components/sync/model/data_batch.h"
 #include "components/sync/model/data_type_error_handler.h"
 #include "components/sync/model/metadata_batch.h"
 #include "components/sync/model/metadata_change_list.h"
 #include "components/sync/model/model_type_change_processor.h"
 #include "components/sync/model/model_type_sync_bridge.h"
 #include "components/sync/model/sync_error.h"
 #include "components/sync/protocol/model_type_state.pb.h"
 #include "components/sync/protocol/sync.pb.h"
 
 namespace syncer {
-struct ActivationContext;
 class CommitQueue;
 class ProcessorEntityTracker;
 
 // A sync component embedded on the synced type's thread that helps to handle
 // communication between sync and model type threads.
 class SharedModelTypeProcessor : public ModelTypeProcessor,
                                  public ModelTypeChangeProcessor,
                                  base::NonThreadSafe {
  public:
   SharedModelTypeProcessor(ModelType type, ModelTypeSyncBridge* bridge);
@@ skipping 140 matching lines @@
   // OnSyncStarting has been called. This pointer is not owned.
   std::unique_ptr<DataTypeErrorHandler> error_handler_;
 
   // WeakPtrFactory for this processor which will be sent to sync thread.
   base::WeakPtrFactory<SharedModelTypeProcessor> weak_ptr_factory_;
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_MODEL_IMPL_SHARED_MODEL_TYPE_PROCESSOR_H_