Introduce read buffer for external strings when using charAt (ia32).

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 82 matching lines @@
     return v8::ThrowException(v8::String::New(
         "externalizeString() can't externalize twice."));
   }
   if (string->IsAsciiRepresentation() && !force_two_byte) {
     char* data = new char[string->length()];
     String::WriteToFlat(*string, data, 0, string->length());
     SimpleAsciiStringResource* resource = new SimpleAsciiStringResource(
         data, string->length());
     result = string->MakeExternal(resource);
     if (result && !string->IsSymbol()) {
-      HEAP->external_string_table()->AddString(*string);
+      if (string->IsSlicedString()) {
+        HEAP->external_string_table()->AddString(
+            SlicedString::cast(*string)->parent());
+      } else {
+        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->IsSymbol()) {
-      HEAP->external_string_table()->AddString(*string);
+      if (string->IsSlicedString()) {
+        HEAP->external_string_table()->AddString(
+            SlicedString::cast(*string)->parent());
+      } else {
+        HEAP->external_string_table()->AddString(*string);
+      }
     }
     if (!result) delete resource;
   }
   if (!result) {
     return v8::ThrowException(v8::String::New("externalizeString() failed."));
   }
   return v8::Undefined();
 }
 
 
@@ skipping 10 matching lines @@
 
 void ExternalizeStringExtension::Register() {
   static ExternalizeStringExtension* externalize_extension = NULL;
   if (externalize_extension == NULL)
     externalize_extension = new ExternalizeStringExtension;
   static v8::DeclareExtension externalize_extension_declaration(
       externalize_extension);
 }
 
 } }  // namespace v8::internal