[strong] Implement revised strong class semantics

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 28007d73f5e1ce27867312a38e713ef5d6d9cc8a..d2821a4320755d0b2c1d56c9c5a5896291d5f6f2 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -10512,6 +10512,9 @@ void JSFunction::SetInstancePrototype(Handle<JSFunction> function,
       function->set_prototype_or_initial_map(*value);
     } else {
       Handle<Map> new_map = Map::Copy(initial_map, "SetInstancePrototype");
+      if (function->map()->is_strong()) {
+        new_map->set_is_strong();
+      }
       JSFunction::SetInitialMap(function, new_map, value);
 
       // If the function is used as the global Array function, cache the
@@ -10636,6 +10639,9 @@ void JSFunction::EnsureHasInitialMap(Handle<JSFunction> function) {
     in_object_properties = function->shared()->CalculateInObjectProperties();
   }
   Handle<Map> map = isolate->factory()->NewMap(instance_type, instance_size);
+  if (function->map()->is_strong()) {
+    map->set_is_strong();
+  }
 
   // Fetch or allocate prototype.
   Handle<Object> prototype;
@@ -10649,7 +10655,8 @@ void JSFunction::EnsureHasInitialMap(Handle<JSFunction> function) {
   DCHECK(map->has_fast_object_elements());
 
   // Finally link initial map and constructor function.
-  JSFunction::SetInitialMap(function, map, Handle<JSReceiver>::cast(prototype));
+  DCHECK(prototype->IsJSReceiver());
+  JSFunction::SetInitialMap(function, map, prototype);
 
   if (!function->shared()->is_generator()) {
     function->StartInobjectSlackTracking();