Convert String to a class.

runtime/vm/snapshot.cc

Index: runtime/vm/snapshot.cc
diff --git a/runtime/vm/snapshot.cc b/runtime/vm/snapshot.cc
index 5f6f4b7991445e428f96a7b6e88be0a1b2223d75..7a99d4bd5fb22c219977869b1480e8c03f94b75e 100644
--- a/runtime/vm/snapshot.cc
+++ b/runtime/vm/snapshot.cc
@@ -66,7 +66,7 @@ static RawType* GetType(ObjectStore* object_store, int index) {
     case kDoubleType: return object_store->double_type();
     case kIntType: return object_store->int_type();
     case kBoolType: return object_store->bool_type();
-    case kStringInterface: return object_store->string_interface();
+    case kStringType: return object_store->string_type();
     case kListInterface: return object_store->list_interface();
     default: break;
   }
@@ -99,8 +99,8 @@ static int GetTypeIndex(ObjectStore* object_store, const RawType* raw_type) {
     return kIntType;
   } else if (raw_type == object_store->bool_type()) {
     return kBoolType;
-  } else if (raw_type == object_store->string_interface()) {
-    return kStringInterface;
+  } else if (raw_type == object_store->string_type()) {
+    return kStringType;
   } else if (raw_type == object_store->list_interface()) {
     return kListInterface;
   }