Add the InvalidationState struct to bundle local state about invalidations.

sync/notifier/invalidation_state_tracker.h

 // Copyright (c) 2012 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.
 //
 // An InvalidationVersionTracker is an interface that handles getting
 // and setting (persisting) max invalidation versions.
 
 #ifndef SYNC_NOTIFIER_INVALIDATION_STATE_TRACKER_H_
 #define SYNC_NOTIFIER_INVALIDATION_STATE_TRACKER_H_
 
 #include <map>
 
 #include "base/basictypes.h"
 #include "google/cacheinvalidation/include/types.h"
 #include "sync/notifier/invalidation_util.h"
 
 namespace syncer {
 
-typedef std::map<invalidation::ObjectId, int64, ObjectIdLessThan>
-    InvalidationVersionMap;
+struct InvalidationState {
+  int64 version;
+};
+
+typedef std::map<invalidation::ObjectId, InvalidationState, ObjectIdLessThan>
+    InvalidationStateMap;
 
 class InvalidationStateTracker {
  public:
   InvalidationStateTracker() {}
 
-  virtual InvalidationVersionMap GetAllMaxVersions() const = 0;
+  virtual InvalidationStateMap GetAllInvalidationStates() const = 0;
 
   // |max_version| should be strictly greater than any existing max
   // version for |model_type|.
   virtual void SetMaxVersion(const invalidation::ObjectId& id,
                              int64 max_version) = 0;
   // Removes all state tracked for |ids|.
   virtual void Forget(const ObjectIdSet& ids) = 0;
 
   // Used by invalidation::InvalidationClient for persistence. |data| is an
   // opaque blob that an invalidation client can use after a restart to
   // bootstrap itself. |data| is binary data (not valid UTF8, embedded nulls,
   // etc).
   virtual void SetBootstrapData(const std::string& data) = 0;
   virtual std::string GetBootstrapData() const = 0;
 
  protected:
   virtual ~InvalidationStateTracker() {}
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_NOTIFIER_INVALIDATION_STATE_TRACKER_H_