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

components/sync/model_impl/processor_entity_tracker.cc

 // 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.
 
 #include "components/sync/model_impl/processor_entity_tracker.h"
 
 #include "base/base64.h"
 #include "base/sha1.h"
 #include "base/trace_event/memory_usage_estimator.h"
 #include "components/sync/base/time.h"
@@ skipping 27 matching lines @@
   metadata.set_server_version(kUncommittedVersion);
   metadata.set_creation_time(TimeToProtoTime(creation_time));
 
   return std::unique_ptr<ProcessorEntityTracker>(
       new ProcessorEntityTracker(storage_key, &metadata));
 }
 
 std::unique_ptr<ProcessorEntityTracker>
 ProcessorEntityTracker::CreateFromMetadata(const std::string& storage_key,
                                            sync_pb::EntityMetadata* metadata) {
+  DCHECK(!storage_key.empty());
   return std::unique_ptr<ProcessorEntityTracker>(
       new ProcessorEntityTracker(storage_key, metadata));
 }
 
 ProcessorEntityTracker::ProcessorEntityTracker(
     const std::string& storage_key,
     sync_pb::EntityMetadata* metadata)
     : storage_key_(storage_key),
       commit_requested_sequence_number_(metadata->acked_sequence_number()) {
   DCHECK(metadata->has_client_tag_hash());
   DCHECK(metadata->has_creation_time());
   metadata_.Swap(metadata);
 }
 
 ProcessorEntityTracker::~ProcessorEntityTracker() {}
 
-void ProcessorEntityTracker::SetStorageKey(const std::string& new_key) {
-  storage_key_ = new_key;
+void ProcessorEntityTracker::SetStorageKey(const std::string& storage_key) {
+  DCHECK(storage_key_.empty());
+  DCHECK(!storage_key.empty());
+  storage_key_ = storage_key;
 }
 
 void ProcessorEntityTracker::SetCommitData(EntityData* data) {
   DCHECK(data);
   // Update data's fields from metadata.
   data->client_tag_hash = metadata_.client_tag_hash();
   if (!metadata_.server_id().empty())
     data->id = metadata_.server_id();
   data->creation_time = ProtoTimeToTime(metadata_.creation_time());
   data->modification_time = ProtoTimeToTime(metadata_.modification_time());
@@ skipping 189 matching lines @@
 void ProcessorEntityTracker::UpdateSpecificsHash(
     const sync_pb::EntitySpecifics& specifics) {
   if (specifics.ByteSize() > 0) {
     HashSpecifics(specifics, metadata_.mutable_specifics_hash());
   } else {
     metadata_.clear_specifics_hash();
   }
 }
 
 }  // namespace syncer