Fix assertion failure caused by external strings.

src/extensions/externalize-string-extension.cc

 // Copyright 2010 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 89 matching lines @@
         args.GetIsolate(),
         "externalizeString() can't externalize twice."));
     return;
   }
   if (string->IsOneByteRepresentation() && !force_two_byte) {
     uint8_t* data = new uint8_t[string->length()];
     String::WriteToFlat(*string, data, 0, string->length());
     SimpleAsciiStringResource* resource = new SimpleAsciiStringResource(
         reinterpret_cast<char*>(data), string->length());
     result = string->MakeExternal(resource);
-    if (result && !string->IsInternalizedString()) {
+    if (result) {
       i::Isolate* isolate = reinterpret_cast<i::Isolate*>(args.GetIsolate());
       isolate->heap()->external_string_table()->AddString(*string);
     }
     if (!result) delete resource;
   } else {
     uc16* data = new uc16[string->length()];
     String::WriteToFlat(*string, data, 0, string->length());
     SimpleTwoByteStringResource* resource = new SimpleTwoByteStringResource(
         data, string->length());
     result = string->MakeExternal(resource);
-    if (result && !string->IsInternalizedString()) {
+    if (result) {
       i::Isolate* isolate = reinterpret_cast<i::Isolate*>(args.GetIsolate());
       isolate->heap()->external_string_table()->AddString(*string);
     }
     if (!result) delete resource;
   }
   if (!result) {
     args.GetIsolate()->ThrowException(v8::String::NewFromUtf8(
         args.GetIsolate(), "externalizeString() failed."));
     return;
   }
 }
 
 
 void ExternalizeStringExtension::IsAscii(
     const v8::FunctionCallbackInfo<v8::Value>& args) {
   if (args.Length() != 1 || !args[0]->IsString()) {
     args.GetIsolate()->ThrowException(v8::String::NewFromUtf8(
         args.GetIsolate(),
         "isAsciiString() requires a single string argument."));
     return;
   }
   bool is_one_byte =
       Utils::OpenHandle(*args[0].As<v8::String>())->IsOneByteRepresentation();
   args.GetReturnValue().Set(is_one_byte);
 }
 
 } }  // namespace v8::internal