[Sync] USS: Filter out redundant changes in SMTP.

sync/internal_api/public/processor_entity_tracker.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 SYNC_INTERNAL_API_PUBLIC_PROCESSOR_ENTITY_TRACKER_H_
 #define SYNC_INTERNAL_API_PUBLIC_PROCESSOR_ENTITY_TRACKER_H_
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 98 matching lines @@
   // Clears any in-memory sync state associated with outstanding commits.
   void ClearTransientSyncState();
 
   // Takes the passed commit data and caches it in the instance.
   // The data is swapped from the input struct without copying.
   void CacheCommitData(EntityData* data);
 
   // Check if the instance has cached commit data.
   bool HasCommitData() const;
 
+  // Check whether |specifics| matches the stored specifics_hash.
+  bool MatchesSpecificsHash(const sync_pb::EntitySpecifics& specifics) const;
+
  private:
   friend class ProcessorEntityTrackerTest;
 
   // The constructor swaps the data from the passed metadata.
   ProcessorEntityTracker(const std::string& client_tag,
                          sync_pb::EntityMetadata* metadata);
 
   // Whether knowledge of this entity has never gone past the processor. This
   // means that no commits have been queued and it did not originate at the
   // server. This is used to determine whether it is safe to delete the tracker
@@ skipping 21 matching lines @@
 
   // TODO(stanisc): this should be removed.
   // The name of the encryption key used to encrypt this item on the server.
   // Empty when no encryption is in use.
   std::string encryption_key_name_;
 };
 
 }  // namespace syncer_v2
 
 #endif  // SYNC_INTERNAL_API_PUBLIC_PROCESSOR_ENTITY_TRACKER_H_