Verify a bit more about external strings

src/objects.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.
 
 #ifndef V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 
 #include "src/allocation.h"
@@ skipping 9269 matching lines @@
 // external resource.  It is important to ensure (externally) that the
 // resource is not deallocated while the ExternalString is live in the
 // V8 heap.
 //
 // The API expects that all ExternalStrings are created through the
 // API.  Therefore, ExternalStrings should not be used internally.
 class ExternalString: public String {
  public:
   DECLARE_CAST(ExternalString)
 
+  inline const void* resource_data() const;
+
   // Layout description.
   static const int kResourceOffset = POINTER_SIZE_ALIGN(String::kSize);
   static const int kShortSize = kResourceOffset + kPointerSize;
   static const int kResourceDataOffset = kResourceOffset + kPointerSize;
   static const int kSize = kResourceDataOffset + kPointerSize;
 
   static const int kMaxShortLength =
       (kShortSize - SeqString::kHeaderSize) / kCharSize;
 
   // Return whether external string is short (data pointer is not cached).
   inline bool is_short();
 
   STATIC_ASSERT(kResourceOffset == Internals::kStringResourceOffset);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalString);
 };
 
 
 // The ExternalOneByteString class is an external string backed by an
 // one-byte string.
 class ExternalOneByteString : public ExternalString {
  public:
   static const bool kHasOneByteEncoding = true;
 
   typedef v8::String::ExternalOneByteStringResource Resource;
 
   // The underlying resource.
-  inline const Resource* resource();
+  inline const Resource* resource() const;
   inline void set_resource(const Resource* buffer);
 
   // Update the pointer cache to the external character array.
   // The cached pointer is always valid, as the external character array does =
   // not move during lifetime.  Deserialization is the only exception, after
   // which the pointer cache has to be refreshed.
   inline void update_data_cache();
 
   inline const uint8_t* GetChars();
 
@@ skipping 15 matching lines @@
 
 // The ExternalTwoByteString class is an external string backed by a UTF-16
 // encoded string.
 class ExternalTwoByteString: public ExternalString {
  public:
   static const bool kHasOneByteEncoding = false;
 
   typedef v8::String::ExternalStringResource Resource;
 
   // The underlying string resource.
-  inline const Resource* resource();
+  inline const Resource* resource() const;
   inline void set_resource(const Resource* buffer);
 
   // Update the pointer cache to the external character array.
   // The cached pointer is always valid, as the external character array does =
   // not move during lifetime.  Deserialization is the only exception, after
   // which the pointer cache has to be refreshed.
   inline void update_data_cache();
 
   inline const uint16_t* GetChars();
 
@@ skipping 1514 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_