Reland "Handlify concat string and substring."

src/factory.h

 // Copyright 2012 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 140 matching lines @@
   // characters of the string are uninitialized. Currently used in regexp code
   // only, where they are pretenured.
   Handle<SeqOneByteString> NewRawOneByteString(
       int length,
       PretenureFlag pretenure = NOT_TENURED);
   Handle<SeqTwoByteString> NewRawTwoByteString(
       int length,
       PretenureFlag pretenure = NOT_TENURED);
 
   // Create a new cons string object which consists of a pair of strings.
-  Handle<String> NewConsString(Handle<String> first,
-                               Handle<String> second);
+  Handle<String> NewConsString(Handle<String> left,
+                               Handle<String> right);
+
+  Handle<ConsString> NewRawConsString(String::Encoding encoding);
 
   // Create a new sequential string containing the concatenation of the inputs.
   Handle<String> NewFlatConcatString(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 proper substring of a string.
   Handle<String> NewProperSubString(Handle<String> str,
                                     int begin,
                                     int end);
 
+  // Create a new string object which holds a substring of a string.
+  Handle<String> NewSubString(Handle<String> str, int begin, int end) {
+    if (begin == 0 && end == str->length()) return str;
+    return NewProperSubString(str, begin, end);
+  }
+
+  Handle<SlicedString> NewRawSlicedString(String::Encoding encoding);
+
   // 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(
       const ExternalAsciiString::Resource* resource);
   Handle<String> NewExternalStringFromTwoByte(
       const ExternalTwoByteString::Resource* resource);
 
   // Create a symbol.
@@ skipping 400 matching lines @@
                           isolate());
   } else {
     return NewNumber(static_cast<double>(value), pretenure);
   }
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_FACTORY_H_