Reintroduce duplicate identifier detection in preparser.

src/conversions.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 107 matching lines @@
 double StringToDouble(UnicodeCache* unicode_cache,
                       Vector<const uc16> str,
                       int flags,
                       double empty_string_val = 0);
 // This version expects a zero-terminated character array.
 double StringToDouble(UnicodeCache* unicode_cache,
                       const char* str,
                       int flags,
                       double empty_string_val = 0);
 
+const int kDoubleToCStringMinBufferSize = 100;
+
 // Converts a double to a string value according to ECMA-262 9.8.1.
 // The buffer should be large enough for any floating point number.
 // 100 characters is enough.
 const char* DoubleToCString(double value, Vector<char> buffer);
 
 // Convert an int to a null-terminated string. The returned string is
 // located inside the buffer, but not necessarily at the start.
 const char* IntToCString(int n, Vector<char> buffer);
 
 // Additional number to string conversions for the number type.
 // The caller is responsible for calling free on the returned pointer.
 char* DoubleToFixedCString(double value, int f);
 char* DoubleToExponentialCString(double value, int f);
 char* DoubleToPrecisionCString(double value, int f);
 char* DoubleToRadixCString(double value, int radix);
 
 } }  // namespace v8::internal
 
 #endif  // V8_CONVERSIONS_H_