Add pointer cache field to external string for access in generated code.

src/objects.h

 // Copyright 2011 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 6740 matching lines @@
 //
 // The API expects that all ExternalStrings are created through the
 // API.  Therefore, ExternalStrings should not be used internally.
 class ExternalString: public String {
  public:
   // Casting
   static inline ExternalString* cast(Object* obj);
 
   // Layout description.
   static const int kResourceOffset = POINTER_SIZE_ALIGN(String::kSize);
-  static const int kSize = kResourceOffset + kPointerSize;
+  static const int kResourceDataOffset = kResourceOffset + kPointerSize;
+  static const int kSize = kResourceDataOffset + kPointerSize;
+
+  // Clear the cached pointer to the character array provided by the resource.
+  // This cache is updated the first time the character array is accessed.
+  inline void clear_data_cache();
 
   STATIC_CHECK(kResourceOffset == Internals::kStringResourceOffset);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalString);
 };
 
 
 // The ExternalAsciiString class is an external string backed by an
 // ASCII string.
 class ExternalAsciiString: public ExternalString {
  public:
   static const bool kHasAsciiEncoding = true;
 
   typedef v8::String::ExternalAsciiStringResource Resource;
 
   // The underlying resource.
   inline const Resource* resource();
   inline void set_resource(const Resource* buffer);
 
+  inline const char* GetChars();
+
   // Dispatched behavior.
   uint16_t ExternalAsciiStringGet(int index);
 
   // Casting.
   static inline ExternalAsciiString* cast(Object* obj);
 
   // Garbage collection support.
   inline void ExternalAsciiStringIterateBody(ObjectVisitor* v);
 
   template<typename StaticVisitor>
@@ skipping 17 matching lines @@
 class ExternalTwoByteString: public ExternalString {
  public:
   static const bool kHasAsciiEncoding = false;
 
   typedef v8::String::ExternalStringResource Resource;
 
   // The underlying string resource.
   inline const Resource* resource();
   inline void set_resource(const Resource* buffer);
 
+  inline const uint16_t* GetChars();
+
   // Dispatched behavior.
   uint16_t ExternalTwoByteStringGet(int index);
 
   // For regexp code.
   const uint16_t* ExternalTwoByteStringGetData(unsigned start);
 
   // Casting.
   static inline ExternalTwoByteString* cast(Object* obj);
 
   // Garbage collection support.
@@ skipping 1049 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_