[Sync] Adding storage key concept for ModelTypeServices.

components/sync/core/data_batch_impl.h

Index: components/sync/core/data_batch_impl.h
diff --git a/components/sync/core/data_batch_impl.h b/components/sync/core/data_batch_impl.h
index ad1f73ddd24daa72568f4aaecb80e80c09b74f05..1e5dad8c8180e1e77ccd27f5bd035c4c76223044 100644
--- a/components/sync/core/data_batch_impl.h
+++ b/components/sync/core/data_batch_impl.h
@@ -21,25 +21,25 @@ namespace syncer_v2 {
 // An implementation of DataBatch that's purpose is to transfer ownership of
 // EntityData objects. As soon as this batch recieves the EntityData, it owns
 // them until Next() is invoked, when it gives up ownerhsip. Because a vector
-// is used internally, this impl is unaware when duplcate client_tags are used,
+// is used internally, this impl is unaware when duplcate storage_keys are used,
 // and it is the caller's job to avoid this.
 class SYNC_EXPORT DataBatchImpl : public DataBatch {
  public:
   DataBatchImpl();
   ~DataBatchImpl() override;
 
-  // Takes ownership of the data tied to a given tag used for storage. Put
-  // should be called at most once for any given client_tag. Data will be
+  // Takes ownership of the data tied to a given key used for storage. Put
+  // should be called at most once for any given storfage_key. Data will be
   // readable in the same order that they are put into the batch.
-  void Put(const std::string& client_tag,
+  void Put(const std::string& storage_key,
            std::unique_ptr<EntityData> entity_data);
 
   // DataBatch implementation.
   bool HasNext() const override;
-  TagAndData Next() override;
+  KeyAndData Next() override;
 
  private:
-  std::vector<TagAndData> tag_data_pairs_;
+  std::vector<KeyAndData> key_data_pairs_;
   size_t read_index_ = 0;
 
   DISALLOW_COPY_AND_ASSIGN(DataBatchImpl);