[regexp] Properly flatten string during initialization

src/factory.h

 // Copyright 2014 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_FACTORY_H_
 #define V8_FACTORY_H_
 
 #include "src/feedback-vector.h"
 #include "src/globals.h"
 #include "src/isolate.h"
@@ skipping 234 matching lines @@
       PretenureFlag pretenure = NOT_TENURED);
 
   // Creates a single character string where the character has given code.
   // A cache is used for Latin1 codes.
   Handle<String> LookupSingleCharacterStringFromCode(uint32_t code);
 
   // Create a new cons string object which consists of a pair of strings.
   MUST_USE_RESULT MaybeHandle<String> NewConsString(Handle<String> left,
                                                     Handle<String> right);
 
+  MUST_USE_RESULT Handle<String> NewConsString(Handle<String> left,
+                                               Handle<String> right, int length,
+                                               bool one_byte);
+
   // Create or lookup a single characters tring made up of a utf16 surrogate
   // pair.
   Handle<String> NewSurrogatePairString(uint16_t lead, uint16_t trail);
 
   // 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.
@@ skipping 576 matching lines @@
   void SetStrictFunctionInstanceDescriptor(Handle<Map> map,
                                            FunctionMode function_mode);
 
   void SetClassFunctionInstanceDescriptor(Handle<Map> map);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_FACTORY_H_