Add cast to make Win-64 compile without warnings.

src/string-search.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 316 matching lines @@
       if (index > subject_length - pattern_length) {
         return -1;
       }
     }
     while (j >= 0 && pattern[j] == (c = subject[index + j])) j--;
     if (j < 0) {
       return index;
     } else if (j < start) {
       // we have matched more than our tables allow us to be smart about.
       // Fall back on BMH shift.
-      index +=
-          pattern_length - 1 - CharOccurrence(bad_char_occurence, last_char);
+      index += pattern_length - 1
+          - CharOccurrence(bad_char_occurence,
+                           static_cast<SubjectChar>(last_char));
     } else {
       int gs_shift = good_suffix_shift[j + 1];
       int bc_occ =
           CharOccurrence(bad_char_occurence, c);
       int shift = j - bc_occ;
       if (gs_shift > shift) {
         shift = gs_shift;
       }
       index += shift;
     }
@@ skipping 76 matching lines @@
     int start_index) {
   Vector<const PatternChar> pattern = search->pattern_;
   int subject_length = subject.length();
   int pattern_length = pattern.length();
   int* char_occurrences = search->bad_char_table();
   int badness = -pattern_length;
 
   // How bad we are doing without a good-suffix table.
   PatternChar last_char = pattern[pattern_length - 1];
   int last_char_shift = pattern_length - 1 -
-      CharOccurrence(char_occurrences, last_char);
+      CharOccurrence(char_occurrences, static_cast<SubjectChar>(last_char));
   // Perform search
   int index = start_index;  // No matches found prior to this index.
   while (index <= subject_length - pattern_length) {
     int j = pattern_length - 1;
     int subject_char;
     while (last_char != (subject_char = subject[index + j])) {
       int bc_occ = CharOccurrence(char_occurrences, subject_char);
       int shift = j - bc_occ;
       index += shift;
       badness += 1 - shift;  // at most zero, so badness cannot increase.
@@ skipping 116 matching lines @@
 static int SearchString(Vector<const SubjectChar> subject,
                         Vector<const PatternChar> pattern,
                         int start_index) {
   StringSearch<PatternChar, SubjectChar> search(pattern);
   return search.Search(subject, start_index);
 }
 
 }}  // namespace v8::internal
 
 #endif  // V8_STRING_SEARCH_H_