components: Cleanup class/struct fwd declarations

components/invalidation/impl/invalidation_logger.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_IMPL_INVALIDATION_LOGGER_H_
 #define COMPONENTS_INVALIDATION_IMPL_INVALIDATION_LOGGER_H_
 
 #include <map>
 #include <set>
 
 #include "base/macros.h"
 #include "base/observer_list.h"
 #include "components/invalidation/public/invalidation_util.h"
 #include "components/invalidation/public/invalidator_state.h"
 
 namespace base {
 class DictionaryValue;
 }  // namespace base
 
 namespace syncer {
-class InvalidationHandler;
 class ObjectIdInvalidationMap;
 }  // namespace syncer
 
 namespace invalidation {
 
 class InvalidationLoggerObserver;
 
 // This class is in charge of logging invalidation-related information.
 // It is used store the state of the InvalidatorService that owns this object
 // and then rebroadcast it to observers than can display it accordingly
@@ skipping 61 matching lines @@
   // necessarily the same as the keys of latest_ids_, because they might
   // have not registered any object id).
   std::multiset<std::string> registered_handlers_;
 
   DISALLOW_COPY_AND_ASSIGN(InvalidationLogger);
 };
 
 }  // namespace invalidation
 
 #endif  // COMPONENTS_INVALIDATION_IMPL_INVALIDATION_LOGGER_H_