[Sync] USS: Implement SimpleMetadataChangeList.

sync/internal_api/public/simple_metadata_change_list.h

 // Copyright 2015 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_SIMPLE_METADATA_CHANGE_LIST_H_
 #define SYNC_INTERNAL_API_PUBLIC_SIMPLE_METADATA_CHANGE_LIST_H_
 
+#include <map>
 #include <string>
 
 #include "sync/api/metadata_change_list.h"
 #include "sync/api/model_type_store.h"
 #include "sync/base/sync_export.h"
+#include "sync/internal_api/public/non_blocking_sync_common.h"
+#include "sync/protocol/data_type_state.pb.h"
+#include "sync/protocol/entity_metadata.pb.h"
 
 namespace syncer_v2 {
 
 // A MetadataChangeList implementation that is meant to be used in combination

[maxbogue, 2016/02/12 18:06:57]

I'm leaving this comment as-is for now until we split out the batch stuff.

 // with a ModelTypeStore. It accumulates changes in member fields, and then when
 // requested transfers them to the store/write batch.
 class SYNC_EXPORT SimpleMetadataChangeList : public MetadataChangeList {
  public:
+  enum ChangeType { UPDATE, CLEAR };
+
+  struct MetadataChange {
+    ChangeType type;
+    sync_pb::EntityMetadata metadata;
+  };
+
+  struct DataTypeStateChange {
+    ChangeType type;
+    sync_pb::DataTypeState state;
+  };
+
+  typedef std::map<std::string, MetadataChange> MetadataChanges;
+
   SimpleMetadataChangeList();
   ~SimpleMetadataChangeList() override;
 
   void UpdateDataTypeState(
       const sync_pb::DataTypeState& data_type_state) override;
   void ClearDataTypeState() override;
   void UpdateMetadata(const std::string& client_tag,
                       const sync_pb::EntityMetadata& metadata) override;
   void ClearMetadata(const std::string& client_tag) override;
 
+  const MetadataChanges& GetMetadataChanges() const;

[pavely, 2016/02/17 00:56:40]

Do you plan to call these functions from outside of TransferChanges()? If not
then they should be private.

[maxbogue, 2016/02/17 19:31:42]

They're gonna be called in tests, yes. TransferChanges is gonna be in its own
class.

+  bool HasDataTypeStateChange() const;
+  const DataTypeStateChange& GetDataTypeStateChange() const;
+
   // Moves all currently accumulated changes into the write batch, clear out
   // local copies. Calling this multiple times will work, but should not be
   // necessary.
-  void TranfserChanges(ModelTypeStore* store,
+  void TransferChanges(ModelTypeStore* store,
                        ModelTypeStore::WriteBatch* write_batch);
+
+ private:
+  MetadataChanges metadata_changes_;
+  scoped_ptr<DataTypeStateChange> state_change_;
 };
 
 }  // namespace syncer_v2
 
 #endif  // SYNC_INTERNAL_API_PUBLIC_SIMPLE_METADATA_CHANGE_LIST_H_