Fix illegal escape-sequences to throw syntax errors.

src/scanner.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 502 matching lines @@
   Token::Value SkipSingleLineComment();
   Token::Value SkipMultiLineComment();
   // Scans a possible HTML comment -- begins with '<!'.
   Token::Value ScanHtmlComment();
 
   void ScanDecimalDigits();
   Token::Value ScanNumber(bool seen_period);
   Token::Value ScanIdentifierOrKeyword();
   Token::Value ScanIdentifierSuffix(LiteralScope* literal);
 
-  void ScanEscape();
   Token::Value ScanString();
 
-  // Decodes a unicode escape-sequence which is part of an identifier.
+  // Scans an escape-sequence which is part of a string and adds the
+  // decoded character to the current literal. Returns true if a pattern
+  // is scanned.
+  bool ScanEscape();
+  // Decodes a Unicode escape-sequence which is part of an identifier.
   // If the escape sequence cannot be decoded the result is kBadChar.
   uc32 ScanIdentifierUnicodeEscape();
-  // Recognizes a uniocde escape-sequence and adds its characters,
+  // Scans a Unicode escape-sequence and adds its characters,
   // uninterpreted, to the current literal. Used for parsing RegExp
   // flags.
   bool ScanLiteralUnicodeEscape();
 
   // Return the current source position.
   int source_pos() {
     return source_->pos() - kCharacterLookaheadBufferSize;
   }
 
   UnicodeCache* unicode_cache_;
@@ skipping 24 matching lines @@
   bool has_multiline_comment_before_next_;
   // Whether we scan 'let' as a keyword for harmony block-scoped let bindings.
   bool harmony_scoping_;
   // Whether we scan 'module', 'import', 'export' as keywords.
   bool harmony_modules_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_SCANNER_H_