Fix Win64 compilation problem.

src/spaces.h

Index: src/spaces.h
diff --git a/src/spaces.h b/src/spaces.h
index 02982cfddcf9d6b20aa9243e9fde82dc7334f8c9..e7e11db55f7e9de7c91342e13f6268a74454514e 100644
--- a/src/spaces.h
+++ b/src/spaces.h
@@ -1745,7 +1745,7 @@ class PagedSpace : public Space {
     first_unswept_page_ = first;
   }
 
-  void IncrementUnsweptFreeBytes(int by) {
+  void IncrementUnsweptFreeBytes(intptr_t by) {
     unswept_free_bytes_ += by;
   }
 
@@ -1754,7 +1754,7 @@ class PagedSpace : public Space {
     unswept_free_bytes_ += (p->area_size() - p->LiveBytes());
   }
 
-  void DecrementUnsweptFreeBytes(int by) {
+  void DecrementUnsweptFreeBytes(intptr_t by) {
     unswept_free_bytes_ -= by;
   }