Correctly stringify mixed encoding indirect strings.

src/json-stringifier.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 817 matching lines @@
 Vector<const uc16> BasicJsonStringifier::GetCharVector(Handle<String> string) {
   String::FlatContent flat = string->GetFlatContent();
   ASSERT(flat.IsTwoByte());
   return flat.ToUC16Vector();
 }
 
 
 void BasicJsonStringifier::SerializeString(Handle<String> object) {
   object = FlattenGetString(object);
   if (is_ascii_) {
-    if (object->IsOneByteRepresentation()) {
+    if (object->IsOneByteRepresentationUnderneath()) {
       SerializeString_<true, uint8_t>(object);
     } else {
       ChangeEncoding();
       SerializeString(object);
     }
   } else {
-    if (object->IsOneByteRepresentation()) {
+    if (object->IsOneByteRepresentationUnderneath()) {
       SerializeString_<false, uint8_t>(object);
     } else {
       SerializeString_<false, uc16>(object);
     }
   }
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_JSON_STRINGIFIER_H_