[proxies] use [[GetPrototypeOf]] trap in for-in

src/objects.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <sstream>
 
@@ skipping 8641 matching lines @@
                                     Handle<JSReceiver> receiver,
                                     Handle<JSReceiver> object,
                                     KeyCollectionType type,
                                     PropertyFilter filter,
                                     KeyAccumulator* accumulator) {
   PrototypeIterator::WhereToEnd end = type == OWN_ONLY
                                           ? PrototypeIterator::END_AT_NON_HIDDEN
                                           : PrototypeIterator::END_AT_NULL;
   for (PrototypeIterator iter(isolate, object,
                               PrototypeIterator::START_AT_RECEIVER, end);
-       !iter.IsAtEnd(); iter.Advance()) {
+       !iter.IsAtEnd();) {
     Handle<JSReceiver> current =
         PrototypeIterator::GetCurrent<JSReceiver>(iter);
     Maybe<bool> result = Just(false);  // Dummy initialization.
     if (current->IsJSProxy()) {
       result = JSProxy::OwnPropertyKeys(isolate, receiver,
                                         Handle<JSProxy>::cast(current), filter,
                                         accumulator);
     } else {
       DCHECK(current->IsJSObject());
       result = GetKeysFromJSObject(isolate, receiver,
                                    Handle<JSObject>::cast(current), &filter,
                                    type, accumulator);
     }
     MAYBE_RETURN(result, Nothing<bool>());
     if (!result.FromJust()) break;  // |false| means "stop iterating".
+    if (!iter.AdvanceFollowingProxies(PrototypeIterator::STOP_EARLY)) {
+      return Nothing<bool>();
+    }
   }
   return Just(true);
 }
 
 
 // ES6 9.5.12
 // Returns |true| on success, |nothing| in case of exception.
 // static
 Maybe<bool> JSProxy::OwnPropertyKeys(Isolate* isolate,
                                      Handle<JSReceiver> receiver,
@@ skipping 11170 matching lines @@
   if (cell->value() != *new_value) {
     cell->set_value(*new_value);
     Isolate* isolate = cell->GetIsolate();
     cell->dependent_code()->DeoptimizeDependentCodeGroup(
         isolate, DependentCode::kPropertyCellChangedGroup);
   }
 }
 
 }  // namespace internal
 }  // namespace v8