Inline instance object hash code into object header on 64 bit.

runtime/vm/become.cc

Index: runtime/vm/become.cc
diff --git a/runtime/vm/become.cc b/runtime/vm/become.cc
index 0fddef218f80624f6e39e8f8d80266c4805453ef..7704a4abb61a4b039fb5b1cbc97acd06f4af3c95 100644
--- a/runtime/vm/become.cc
+++ b/runtime/vm/become.cc
@@ -262,12 +262,16 @@ void Become::ElementsForwardIdentity(const Array& before, const Array& after) {
 
     ForwardObjectTo(before_obj, after_obj);
 
+#if defined(HASH_IN_OBJECT_HEADER)
+    Object::SetCachedHash(after_obj, Object::GetCachedHash(before_obj));
+#else
     // Forward the identity hash too if it has one.
     intptr_t hash = heap->GetHash(before_obj);
     if (hash != 0) {
       ASSERT(heap->GetHash(after_obj) == 0);
       heap->SetHash(after_obj, hash);
     }
+#endif
   }
 
   {