Reintroduce duplicate identifier detection in preparser.

src/scanner-base.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 331 matching lines @@
   }
   Vector<const uc16> next_literal_uc16_string() {
     ASSERT_NOT_NULL(next_.literal_chars);
     return next_.literal_chars->uc16_literal();
   }
   int next_literal_length() const {
     ASSERT_NOT_NULL(next_.literal_chars);
     return next_.literal_chars->length();
   }
 
+  UnicodeCache* unicode_cache() { return unicode_cache_; }
+
   static const int kCharacterLookaheadBufferSize = 1;
 
  protected:
   // The current and look-ahead token.
   struct TokenDesc {
     Token::Value token;
     Location location;
     LiteralBuffer* literal_chars;
   };
 
@@ skipping 191 matching lines @@
   // line-terminator after the current token, and before the next.
   bool has_multiline_comment_before_next_;
   // Whether we scan 'let' as a keyword for harmony block scoped
   // let bindings.
   bool harmony_block_scoping_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_SCANNER_BASE_H_