[Sync] Add support for proxy types

sync/syncable/directory_backing_store_unittest.cc

Index: sync/syncable/directory_backing_store_unittest.cc
diff --git a/sync/syncable/directory_backing_store_unittest.cc b/sync/syncable/directory_backing_store_unittest.cc
index 917e874e16cd1f195b2156245c48d31e67467f01..96911978e932a8b75722e6a7107c98f6c4fba62d 100644
--- a/sync/syncable/directory_backing_store_unittest.cc
+++ b/sync/syncable/directory_backing_store_unittest.cc
@@ -3172,10 +3172,12 @@ INSTANTIATE_TEST_CASE_P(DirectoryBackingStore, MigrationTest,
                         testing::Range(67, kCurrentDBVersion));
 
 TEST_F(DirectoryBackingStoreTest, ModelTypeIds) {
-  for (int i = FIRST_REAL_MODEL_TYPE; i < MODEL_TYPE_COUNT; ++i) {
+  ModelTypeSet protocol_types = ProtocolTypes();
+  for (ModelTypeSet::Iterator iter = protocol_types.First(); iter.Good();
+       iter.Inc()) {
     std::string model_id =
-        TestDirectoryBackingStore::ModelTypeEnumToModelId(ModelTypeFromInt(i));
-    EXPECT_EQ(i,
+        TestDirectoryBackingStore::ModelTypeEnumToModelId(iter.Get());
+    EXPECT_EQ(iter.Get(),
         TestDirectoryBackingStore::ModelIdToModelTypeEnum(model_id.data(),
                                                           model_id.size()));
   }