Inctroduce NewStrictSubstring to avoid check for SubString(str, 0, str.length...

src/factory.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 115 matching lines @@
 
   // Create a new cons string object which consists of a pair of strings.
   Handle<String> NewConsString(Handle<String> first,
                                Handle<String> second);
 
   // Create a new string object which holds a substring of a string.
   Handle<String> NewSubString(Handle<String> str,
                               int begin,
                               int end);
 
+  // Create a new string object which holds a strict substring of a string.
+  Handle<String> NewStrictSubString(Handle<String> str,
+                                    int begin,
+                                    int end);
+
   // Creates a new external String object.  There are two String encodings
   // in the system: ASCII and two byte.  Unlike other String types, it does
   // not make sense to have a UTF-8 factory function for external strings,
   // because we cannot change the underlying buffer.
   Handle<String> NewExternalStringFromAscii(
       ExternalAsciiString::Resource* resource);
   Handle<String> NewExternalStringFromTwoByte(
       ExternalTwoByteString::Resource* resource);
 
   // Create a global (but otherwise uninitialized) context.
@@ skipping 296 matching lines @@
   // Update the map cache in the global context with (keys, map)
   Handle<MapCache> AddToMapCache(Handle<Context> context,
                                  Handle<FixedArray> keys,
                                  Handle<Map> map);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_FACTORY_H_