[Sync] Implement support for updating storage key for new entities

components/sync/model_impl/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 COMPONENTS_SYNC_MODEL_IMPL_PROCESSOR_ENTITY_TRACKER_H_
 #define COMPONENTS_SYNC_MODEL_IMPL_PROCESSOR_ENTITY_TRACKER_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 82 matching lines @@
   //
   // Note that the receipt of a successful commit response does not necessarily
   // unset IsUnsynced().  If many local changes occur in quick succession, it's
   // possible that the committed item was already out of date by the time it
   // reached the server.
   void ReceiveCommitResponse(const CommitResponseData& data);
 
   // Clears any in-memory sync state associated with outstanding commits.
   void ClearTransientSyncState();
 
-  // Update storage_key_.
-  // This function should only be called by
-  // ModelTypeChangeProcessor::UpdateStorageKey for the data type which does not
-  // create storage key based on syncer::EntityData.
-  void SetStorageKey(const std::string& new_key);
+  // Update storage_key_. Allows setting storage key for datatypes that don't
+  // generate storage key from syncer::EntityData. Should only be called for
+  // tracker initialized with empty storage key.
+  void SetStorageKey(const std::string& storage_key);
 
   // Takes the passed commit data updates its fields with values from metadata
   // and caches it in the instance. The data is swapped from the input struct
   // without copying.
   void SetCommitData(EntityData* data);
 
   // Caches the a copy of |data_ptr|, which doesn't copy the data itself.
   void CacheCommitData(const EntityDataPtr& data_ptr);
 
   // Check if the instance has cached commit data.
@@ skipping 36 matching lines @@
   // The data is reset once commit confirmation is received.
   EntityDataPtr commit_data_;
 
   // The sequence number of the last item sent to the sync thread.
   int64_t commit_requested_sequence_number_;
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_MODEL_IMPL_PROCESSOR_ENTITY_TRACKER_H_