Fix compilation failure on Win64 since r14020.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 40ba412e15748932f573c5f5ac2eccdd6fd7ae42..7333bbb74287f20fc3ef061d7b2af2533654e34a 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -3880,7 +3880,7 @@ MaybeObject* Heap::CopyCode(Code* code, Vector<byte> reloc_info) {
   Address new_addr = reinterpret_cast<HeapObject*>(result)->address();
 
   // Copy header and instructions.
-  CopyBytes(new_addr, old_addr, relocation_offset);
+  CopyBytes(new_addr, old_addr, static_cast<int>(relocation_offset));
 
   Code* new_code = Code::cast(result);
   new_code->set_relocation_info(ByteArray::cast(reloc_info_array));