Refactor part of handles.cc

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index fe4d089d7918c91c10882030db25675ab77c5e25..360401603b875e01cc2585e8af43540368bc6973 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -2973,10 +2973,24 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_SetCode) {
 RUNTIME_FUNCTION(MaybeObject*, Runtime_SetExpectedNumberOfProperties) {
   HandleScope scope(isolate);
   ASSERT(args.length() == 2);
-  CONVERT_ARG_HANDLE_CHECKED(JSFunction, function, 0);
+  CONVERT_ARG_HANDLE_CHECKED(JSFunction, func, 0);
   CONVERT_SMI_ARG_CHECKED(num, 1);
   RUNTIME_ASSERT(num >= 0);
-  SetExpectedNofProperties(function, num);
+  // If objects constructed from this function exist then changing
+  // 'estimated_nof_properties' is dangerous since the previous value might
+  // have been compiled into the fast construct stub. More over, the inobject
+  // slack tracking logic might have adjusted the previous value, so even
+  // passing the same value is risky.
+  if (func->shared()->live_objects_may_exist()) return;
+
+  func->shared()->set_expected_nof_properties(nof);
+  if (func->has_initial_map()) {
+    Handle<Map> new_initial_map =
+        func->GetIsolate()->factory()->CopyMap(
+            Handle<Map>(func->initial_map()));
+    new_initial_map->set_unused_property_fields(num);
+    func->set_initial_map(*new_initial_map);
+  }
   return isolate->heap()->undefined_value();
 }