components: Cleanup class/struct fwd declarations

components/invalidation/public/invalidation.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_INVALIDATION_PUBLIC_INVALIDATION_H_
 #define COMPONENTS_INVALIDATION_PUBLIC_INVALIDATION_H_
 
 #include <stdint.h>
 
 #include <memory>
 #include <string>
 
 #include "base/memory/weak_ptr.h"
 #include "base/sequenced_task_runner.h"
 #include "base/values.h"
 #include "components/invalidation/public/ack_handle.h"
 #include "components/invalidation/public/invalidation_export.h"
 #include "google/cacheinvalidation/include/types.h"
 
 namespace syncer {
 
-class DroppedInvalidationTracker;
 class AckHandler;
 
 // Represents a local invalidation, and is roughly analogous to
 // invalidation::Invalidation.  Unlike invalidation::Invalidation, this class
 // supports "local" ack-tracking and simple serialization to pref values.
 class INVALIDATION_EXPORT Invalidation {
  public:
   // Factory functions.
   static Invalidation Init(const invalidation::ObjectId& id,
                            int64_t version,
@@ skipping 87 matching lines @@
   AckHandle ack_handle_;
 
   // The acknowledgement tracking handler and its thread.
   base::WeakPtr<AckHandler> ack_handler_;
   scoped_refptr<base::SequencedTaskRunner> ack_handler_task_runner_;
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_INVALIDATION_PUBLIC_INVALIDATION_H_