Fix Windows 64 build.

src/json-stringifier.h

 // Copyright 2012 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 569 matching lines @@
     SrcChar c = src[i];
     if (DoNotEscape(c)) {
       *(dest++) = static_cast<DestChar>(c);
     } else {
       const char* chars = &JsonEscapeTable[c * kJsonEscapeTableEntrySize];
       while (*chars != '\0') *(dest++) = *(chars++);
     }
   }
 
   *(dest++) = '"';
-  current_index_ += dest - dest_start;
+  current_index_ += static_cast<int>(dest - dest_start);
 }
 
 
 template <bool is_ascii, typename Char>
 void BasicJsonStringifier::SerializeString_(Vector<const Char> vector,
                                             Handle<String> string) {
   int length = vector.length();
   // We make a rough estimate to find out if the current string can be
   // serialized without allocating a new string part. The worst case length of
   // an escaped character is 6.  Shifting left by 3 is a more pessimistic
@@ skipping 76 matching lines @@
       SerializeString_<false, char>(flat.ToAsciiVector(), object);
     } else {
       SerializeString_<false, uc16>(flat.ToUC16Vector(), object);
     }
   }
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_JSON_STRINGIFIER_H_