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

src/extensions/externalize-string-extension.cc

Index: src/extensions/externalize-string-extension.cc
diff --git a/src/extensions/externalize-string-extension.cc b/src/extensions/externalize-string-extension.cc
index 9fbf3298189acdace28f175af3f855b5ae13bd68..27e16094970151060b1f4478c3051f04be27186f 100644
--- a/src/extensions/externalize-string-extension.cc
+++ b/src/extensions/externalize-string-extension.cc
@@ -100,7 +100,12 @@ v8::Handle<v8::Value> ExternalizeStringExtension::Externalize(
         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 {
@@ -110,7 +115,12 @@ v8::Handle<v8::Value> ExternalizeStringExtension::Externalize(
         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;
   }