[keys] Make for-in great again.

src/keys.h

 // Copyright 2012 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.
 
 #ifndef V8_KEYS_H_
 #define V8_KEYS_H_
 
 #include "src/isolate.h"
 #include "src/objects.h"
 
@@ skipping 35 matching lines @@
   Maybe<bool> CollectKeys(Handle<JSReceiver> receiver,
                           Handle<JSReceiver> object);
   Maybe<bool> CollectOwnElementIndices(Handle<JSReceiver> receiver,
                                        Handle<JSObject> object);
   Maybe<bool> CollectOwnPropertyNames(Handle<JSReceiver> receiver,
                                       Handle<JSObject> object);
   Maybe<bool> CollectAccessCheckInterceptorKeys(
       Handle<AccessCheckInfo> access_check_info, Handle<JSReceiver> receiver,
       Handle<JSObject> object);
 
+  // Might return directly the object's enum_cache, copy the result before using
+  // as an elements backing store for a JSObject.
   static Handle<FixedArray> GetOwnEnumPropertyKeys(Isolate* isolate,
                                                    Handle<JSObject> object);
-
   void AddKey(Object* key, AddKeyConversion convert = DO_NOT_CONVERT);
   void AddKey(Handle<Object> key, AddKeyConversion convert = DO_NOT_CONVERT);
   void AddKeys(Handle<FixedArray> array, AddKeyConversion convert);
   void AddKeys(Handle<JSObject> array_like, AddKeyConversion convert);
 
   // Jump to the next level, pushing the current |levelLength_| to
   // |levelLengths_| and adding a new list to |elements_|.
   Isolate* isolate() { return isolate_; }
   // Filter keys based on their property descriptors.
   PropertyFilter filter() { return filter_; }
@@ skipping 64 matching lines @@
   void set_is_for_in(bool value) { is_for_in_ = value; }
 
   MaybeHandle<FixedArray> GetKeys(
       GetKeysConversion convert = GetKeysConversion::kKeepNumbers);
 
  private:
   void Prepare();
   MaybeHandle<FixedArray> GetKeysFast(GetKeysConversion convert);
   MaybeHandle<FixedArray> GetKeysSlow(GetKeysConversion convert);
 
+  MaybeHandle<FixedArray> GetOwnKeysWithUninitializedEnumCache();
+
   Isolate* isolate_;
   Handle<JSReceiver> receiver_;
   Handle<JSReceiver> last_non_empty_prototype_;
   KeyCollectionMode mode_;
   PropertyFilter filter_;
   bool is_for_in_ = false;
   bool is_receiver_simple_enum_ = false;
   bool has_empty_prototype_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(FastKeyAccumulator);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_KEYS_H_