[runtime] Stop cloning AccessorInfo, just rely on PropertyAttributes for readonly.

The old mechanism was a left-over from a previous time where the runtime
would rely on the presence or absence of the setter to figure out
whether or not the property is mutable. This is unnecessary by now.

Review URL: https://codereview.chromium.org/1600923002

Cr-Commit-Position: refs/heads/master@{#33377}

src/accessors.cc

@@ -41,20 +41,6 @@ Handle<AccessorInfo> Accessors::MakeAccessor(
 }
 
 
-Handle<AccessorInfo> Accessors::CloneAccessor(Isolate* isolate,
-                                              Handle<AccessorInfo> accessor) {
-  Factory* factory = isolate->factory();
-  Handle<AccessorInfo> info = factory->NewAccessorInfo();
-  info->set_name(accessor->name());
-  info->set_flag(accessor->flag());
-  info->set_expected_receiver_type(accessor->expected_receiver_type());
-  info->set_getter(accessor->getter());
-  info->set_setter(accessor->setter());
-  info->set_data(accessor->data());
-  return info;
-}
-
-
 static V8_INLINE bool CheckForName(Handle<Name> name,
                                    Handle<String> property_name,
                                    int offset,

src/accessors.h

@@ -100,9 +100,6 @@ class Accessors : public AllStatic {
       AccessorNameGetterCallback getter,
       AccessorNameSetterCallback setter,
       PropertyAttributes attributes);
-
-  static Handle<AccessorInfo> CloneAccessor(Isolate* isolate,
-                                            Handle<AccessorInfo> accessor);
 };
 
 }  // namespace internal

src/objects.cc

@@ -5204,13 +5204,6 @@ void JSObject::AddProperty(Handle<JSObject> object, Handle<Name> name,
 }
 
 
-// static
-void AccessorInfo::ClearSetter(Handle<AccessorInfo> info) {
-  Handle<Object> object = v8::FromCData(info->GetIsolate(), nullptr);
-  info->set_setter(*object);
-}
-
-
 // Reconfigures a property to a data property with attributes, even if it is not
 // reconfigurable.
 // Requires a LookupIterator that does not look at the prototype chain beyond
@@ -5279,15 +5272,7 @@ Maybe<bool> JSObject::DefineOwnPropertyIgnoreAttributes(
           if (details.attributes() == attributes) return Just(true);
 
           // Reconfigure the accessor if attributes mismatch.
-          Handle<AccessorInfo> new_data = Accessors::CloneAccessor(
-              it->isolate(), Handle<AccessorInfo>::cast(accessors));
-          new_data->set_property_attributes(attributes);
-          // By clearing the setter we don't have to introduce a lookup to
-          // the setter, simply make it unavailable to reflect the
-          // attributes.
-          if (attributes & READ_ONLY) AccessorInfo::ClearSetter(new_data);
-
-          it->TransitionToAccessorPair(new_data, attributes);
+          it->TransitionToAccessorPair(accessors, attributes);
         } else {
           it->ReconfigureDataProperty(value, attributes);
         }

src/objects.h

@@ -10205,8 +10205,6 @@ class AccessorInfo: public Struct {
   // Dispatched behavior.
   DECLARE_PRINTER(AccessorInfo)
 
-  static void ClearSetter(Handle<AccessorInfo> info);
-
   inline bool all_can_read();
   inline void set_all_can_read(bool value);