[Sync] Move sync/{internal_api,syncable} into syncer namespace

sync/internal_api/public/syncable/model_type_test_util.h

Index: sync/internal_api/public/syncable/model_type_test_util.h
diff --git a/sync/internal_api/public/syncable/model_type_test_util.h b/sync/internal_api/public/syncable/model_type_test_util.h
index 173212fde59190351b8a5787217f292a35980fd8..f60e1c0967a8ea21edd9051104dd96ec68992d42 100644
--- a/sync/internal_api/public/syncable/model_type_test_util.h
+++ b/sync/internal_api/public/syncable/model_type_test_util.h
@@ -11,6 +11,7 @@
 #include "sync/internal_api/public/syncable/model_type.h"
 #include "testing/gmock/include/gmock/gmock.h"
 
+namespace syncer {
 namespace syncable {
 
 // Defined for googletest.  Forwards to ModelTypeSetToString().
@@ -22,5 +23,6 @@ void PrintTo(ModelTypeSet model_types, ::std::ostream* os);
 ::testing::Matcher<ModelTypeSet> HasModelTypes(ModelTypeSet expected_types);
 
 }  // namespace syncable
+}  // namespace syncer
 
 #endif  // SYNC_INTERNAL_PUBLIC_API_SYNCABLE_MODEL_TYPE_TEST_UTIL_H_