Fix cast that fails on Win64.

src/runtime.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 4705 matching lines @@
           write_cursor[3] = replacement[3];
           write_cursor[4] = replacement[4];
           write_cursor[5] = replacement[5];
         }
       }
       write_cursor += len;
     }
   }
   *(write_cursor++) = '"';
 
-  int final_length =
+  int final_length = static_cast<int>(
       write_cursor - reinterpret_cast<Char*>(
-          new_string->address() + SeqAsciiString::kHeaderSize);
+          new_string->address() + SeqAsciiString::kHeaderSize));
   Heap::new_space()->ShrinkStringAtAllocationBoundary<StringType>(new_string,
                                                                   final_length);
   return new_string;
 }
 
 
 static MaybeObject* Runtime_QuoteJSONString(Arguments args) {
   NoHandleAllocation ha;
   CONVERT_CHECKED(String, str, args[0]);
   if (!str->IsFlat()) {
@@ skipping 6039 matching lines @@
   } else {
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     Counters::gc_last_resort_from_js.Increment();
     Heap::CollectAllGarbage(false);
   }
 }
 
 
 } }  // namespace v8::internal