Fix warnings on Win64.

src/serialize.h

 // Copyright 2006-2008 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 356 matching lines @@
     memcpy(to, data_ + position_, number_of_bytes);
     position_ += number_of_bytes;
   }
 
   int GetInt() {
     // A little unwind to catch the really small ints.
     int snapshot_byte = Get();
     if ((snapshot_byte & 0x80) == 0) {
       return snapshot_byte;
     }
-    uintptr_t accumulator = (snapshot_byte & 0x7f) << 7;
+    int accumulator = (snapshot_byte & 0x7f) << 7;
     while (true) {
       snapshot_byte = Get();
       if ((snapshot_byte & 0x80) == 0) {
         return accumulator | snapshot_byte;
       }
       accumulator = (accumulator | (snapshot_byte & 0x7f)) << 7;
     }
     UNREACHABLE();
     return accumulator;
   }
@@ skipping 230 matching lines @@
 
   friend class ObjectSerializer;
   friend class Deserializer2;
 
   DISALLOW_COPY_AND_ASSIGN(Serializer2);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_SERIALIZE_H_