Fix Chromium bug 62639.

src/preparser.h

 // Copyright 2010 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 1352 matching lines @@
   int literal_position = scanner_->location().beg_pos;
   log_->LogSymbol(literal_position, literal_chars, literal_length);
 
   return kUnknownExpression;
 }
 
 
 template <typename Scanner, typename Log>
 Identifier PreParser<Scanner, Log>::ParseIdentifier(bool* ok) {
   Expect(i::Token::IDENTIFIER, ok);
+  if (!*ok) return kUnknownIdentifier;
   return GetIdentifierSymbol();
 }
 
 
 template <typename Scanner, typename Log>
 Identifier PreParser<Scanner, Log>::ParseIdentifierName(bool* ok) {
   i::Token::Value next = Next();
   if (i::Token::IsKeyword(next)) {
     int pos = scanner_->location().beg_pos;
     const char* keyword = i::Token::String(next);
@@ skipping 22 matching lines @@
     *is_get = strncmp(token, "get", 3) == 0;
     *is_set = !*is_get && strncmp(token, "set", 3) == 0;
   }
   return GetIdentifierSymbol();
 }
 
 #undef CHECK_OK
 } }  // v8::preparser
 
 #endif  // V8_PREPARSER_H