[Sync] Add sync_export.h (Step 1 for componentizing sync)

sync/internal_api/public/base/model_type_payload_map.h

 // Copyright (c) 2012 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.
 //
 // Definition of ModelTypePayloadMap and various utility functions.
 
 #ifndef SYNC_INTERNAL_PUBLIC_API_BASE_MODEL_TYPE_PAYLOAD_MAP_H_
 #define SYNC_INTERNAL_PUBLIC_API_BASE_MODEL_TYPE_PAYLOAD_MAP_H_
 
 #include <map>
 #include <string>
 
+#include "sync/base/sync_export.h"
 #include "sync/internal_api/public/base/model_type.h"
 
+// TODO(akalin): Move the non-exported functions in this file to a
+// private header.
+
 namespace base {
 class DictionaryValue;
 }
 
 namespace syncer {
 
 // A container that contains a set of datatypes with possible string
 // payloads.
 typedef std::map<ModelType, std::string> ModelTypePayloadMap;
 
 // Helper functions for building ModelTypePayloadMaps.
 
 // Make a TypePayloadMap from all the types in a ModelTypeSet using a
 // default payload.
-ModelTypePayloadMap ModelTypePayloadMapFromEnumSet(
+SYNC_EXPORT ModelTypePayloadMap ModelTypePayloadMapFromEnumSet(
     ModelTypeSet model_types, const std::string& payload);
 
 ModelTypeSet ModelTypePayloadMapToEnumSet(
     const ModelTypePayloadMap& payload_map);
 
 std::string ModelTypePayloadMapToString(
     const ModelTypePayloadMap& model_type_payloads);
 
 // Caller takes ownership of the returned dictionary.
 base::DictionaryValue* ModelTypePayloadMapToValue(
     const ModelTypePayloadMap& model_type_payloads);
 
 // Coalesce |update| into |original|, overwriting only when |update| has
 // a non-empty payload.
 void CoalescePayloads(ModelTypePayloadMap* original,
                       const ModelTypePayloadMap& update);
 
 }  // namespace syncer
 
 #endif  // SYNC_INTERNAL_PUBLIC_API_BASE_MODEL_TYPE_PAYLOAD_MAP_H_