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

sync/internal_api/public/base/model_type_payload_map.h

Index: sync/internal_api/public/base/model_type_payload_map.h
diff --git a/sync/internal_api/public/base/model_type_payload_map.h b/sync/internal_api/public/base/model_type_payload_map.h
index 699b84b3529086ddafea9db56c6b621987dfe99c..528f6228eec880ecf863675756ec0a347bc42156 100644
--- a/sync/internal_api/public/base/model_type_payload_map.h
+++ b/sync/internal_api/public/base/model_type_payload_map.h
@@ -10,6 +10,7 @@
 #include <map>
 #include <string>
 
+#include "sync/base/sync_export.h"
 #include "sync/internal_api/public/base/model_type.h"
 
 namespace base {
@@ -26,23 +27,23 @@ typedef std::map<ModelType, std::string> ModelTypePayloadMap;
 
 // 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(
+SYNC_EXPORT ModelTypeSet ModelTypePayloadMapToEnumSet(
     const ModelTypePayloadMap& payload_map);
 
-std::string ModelTypePayloadMapToString(
+SYNC_EXPORT std::string ModelTypePayloadMapToString(
     const ModelTypePayloadMap& model_type_payloads);
 
 // Caller takes ownership of the returned dictionary.
-base::DictionaryValue* ModelTypePayloadMapToValue(
+SYNC_EXPORT 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);
+SYNC_EXPORT void CoalescePayloads(ModelTypePayloadMap* original,
+                                  const ModelTypePayloadMap& update);
 
 }  // namespace syncer