[ESnext] Implement Object spread

src/objects.h

 // 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.
 
 #ifndef V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 #include <memory>
 
@@ skipping 1984 matching lines @@
 
   static MaybeHandle<Context> GetFunctionRealm(Handle<JSReceiver> receiver);
 
   // Get the first non-hidden prototype.
   static inline MaybeHandle<Object> GetPrototype(Isolate* isolate,
                                                  Handle<JSReceiver> receiver);
 
   MUST_USE_RESULT static Maybe<bool> HasInPrototypeChain(
       Isolate* isolate, Handle<JSReceiver> object, Handle<Object> proto);
 
+  // Reads all enumerable own properties of source and adds them to target,
+  // using either Set or CreateDataProperty depending on the use_set argument.
+  MUST_USE_RESULT static Maybe<bool> SetOrCopyDataProperties(
+      Isolate* isolate, Handle<JSReceiver> target, Handle<Object> source,
+      bool use_set);
+
   // Implementation of [[HasProperty]], ECMA-262 5th edition, section 8.12.6.
   MUST_USE_RESULT static Maybe<bool> HasProperty(LookupIterator* it);
   MUST_USE_RESULT static inline Maybe<bool> HasProperty(
       Handle<JSReceiver> object, Handle<Name> name);
   MUST_USE_RESULT static inline Maybe<bool> HasElement(
       Handle<JSReceiver> object, uint32_t index);
 
   MUST_USE_RESULT static inline Maybe<bool> HasOwnProperty(
       Handle<JSReceiver> object, Handle<Name> name);
   MUST_USE_RESULT static inline Maybe<bool> HasOwnProperty(
@@ skipping 9730 matching lines @@
   }
 };
 
 
 }  // NOLINT, false-positive due to second-order macros.
 }  // NOLINT, false-positive due to second-order macros.
 
 #include "src/objects/object-macros-undef.h"
 
 #endif  // V8_OBJECTS_H_