Fix win64 build.

src/heap.cc

 // 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 2534 matching lines @@
   size_t length = resource->length();
   if (length > static_cast<size_t>(String::kMaxLength)) {
     Top::context()->mark_out_of_memory();
     return Failure::OutOfMemoryException();
   }
 
   // For small strings we check whether the resource contains only
   // ASCII characters.  If yes, we use a different string map.
   static const size_t kAsciiCheckLengthLimit = 32;
   bool is_ascii = length <= kAsciiCheckLengthLimit &&
-      String::IsAscii(resource->data(), length);
+      String::IsAscii(resource->data(), static_cast<int>(length));
   Map* map = is_ascii ?
       Heap::external_string_with_ascii_data_map() : Heap::external_string_map();
   Object* result;
   { MaybeObject* maybe_result = Allocate(map, NEW_SPACE);
     if (!maybe_result->ToObject(&result)) return maybe_result;
   }
 
   ExternalTwoByteString* external_string = ExternalTwoByteString::cast(result);
   external_string->set_length(static_cast<int>(length));
   external_string->set_hash_field(String::kEmptyHashField);
@@ skipping 2934 matching lines @@
 void ExternalStringTable::TearDown() {
   new_space_strings_.Free();
   old_space_strings_.Free();
 }
 
 
 List<Object*> ExternalStringTable::new_space_strings_;
 List<Object*> ExternalStringTable::old_space_strings_;
 
 } }  // namespace v8::internal