Verify a bit more about external strings

include/v8.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /** \mainpage V8 API Reference Guide
  *
  * V8 is Google's open source JavaScript engine.
  *
  * This set of documents provides reference material generated from the
  * V8 header file, include/v8.h.
@@ skipping 2410 matching lines @@
    private:
     uint16_t* str_;
     int length_;
 
     // Disallow copying and assigning.
     Value(const Value&);
     void operator=(const Value&);
   };
 
  private:
-  void VerifyExternalStringResourceBase(ExternalStringResourceBase* v,
+  friend class internal::Heap;
+  void VerifyExternalStringResourceBase(const ExternalStringResourceBase* v,
                                         Encoding encoding) const;
-  void VerifyExternalStringResource(ExternalStringResource* val) const;
   static void CheckCast(v8::Value* obj);
 };
 
 
 /**
  * A JavaScript symbol (ECMA-262 edition 6)
  *
  * This is an experimental feature. Use at your own risk.
  */
 class V8_EXPORT Symbol : public Name {
@@ skipping 5180 matching lines @@
   typedef internal::Internals I;
   O* obj = *reinterpret_cast<O* const*>(this);
   String::ExternalStringResource* result;
   if (I::IsExternalTwoByteString(I::GetInstanceType(obj))) {
     void* value = I::ReadField<void*>(obj, I::kStringResourceOffset);
     result = reinterpret_cast<String::ExternalStringResource*>(value);
   } else {
     result = NULL;
   }
 #ifdef V8_ENABLE_CHECKS
-  VerifyExternalStringResource(result);
+  VerifyExternalStringResourceBase(result, TWO_BYTE_ENCODING);
 #endif
   return result;
 }
 
 
 String::ExternalStringResourceBase* String::GetExternalStringResourceBase(
     String::Encoding* encoding_out) const {
   typedef internal::Object O;
   typedef internal::Internals I;
   O* obj = *reinterpret_cast<O* const*>(this);
@@ skipping 680 matching lines @@
  */
 
 
 }  // namespace v8
 
 
 #undef TYPE_CHECK
 
 
 #endif  // V8_H_