Convert String and List to abstract classes.

runtime/vm/class_finalizer.cc

Index: runtime/vm/class_finalizer.cc
diff --git a/runtime/vm/class_finalizer.cc b/runtime/vm/class_finalizer.cc
index 73be75ac0bbb87bc22cd96ee2b5482db4f15e6d5..5b5aa33a25474be3498c2c55e3109406a73c6196 100644
--- a/runtime/vm/class_finalizer.cc
+++ b/runtime/vm/class_finalizer.cc
@@ -299,14 +299,17 @@ void ClassFinalizer::ResolveSuperType(const Class& cls) {
       case kWeakPropertyCid:
         is_error = true;
         break;
-      default:
+      default: {
         // Special case: classes for which we don't have a known class id.
         // TODO(regis): Why isn't comparing to kIntegerCid enough?
-        if (Type::Handle(Type::Double()).type_class() == super_class.raw() ||
-            Type::Handle(Type::IntType()).type_class() == super_class.raw()) {
+        RawClass* super_raw = super_class.raw();
+        if (Type::Handle(Type::Double()).type_class() == super_raw ||
+            Type::Handle(Type::IntType()).type_class() == super_raw ||
+            Type::Handle(Type::StringType()).type_class() == super_raw) {
           is_error = true;
         }
         break;
+      }
     }
     if (is_error) {
       const Script& script = Script::Handle(cls.script());
@@ -1378,7 +1381,7 @@ void ClassFinalizer::ResolveInterfaces(const Class& cls,
           interface.IsNumberType() ||
           interface.IsIntType() ||
           interface.IsDoubleType() ||
-          interface.IsStringInterface() ||
+          interface.IsStringType() ||
           (interface.IsFunctionType() && !cls.IsSignatureClass()) ||
           interface.IsDynamicType()) {
         const Script& script = Script::Handle(cls.script());