[runtime] JSObject::GetKeys never returns the EnumCache, so we don't need to copy

src/api.cc

 // 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.
 
 #include "src/api.h"
 
 #include <string.h>  // For memcpy, strlen.
 #ifdef V8_USE_ADDRESS_SANITIZER
 #include <sanitizer/asan_interface.h>
 #endif  // V8_USE_ADDRESS_SANITIZER
@@ skipping 3773 matching lines @@
 
 
 MaybeLocal<Array> v8::Object::GetOwnPropertyNames(Local<Context> context) {
   PREPARE_FOR_EXECUTION(context, "v8::Object::GetOwnPropertyNames()", Array);
   auto self = Utils::OpenHandle(this);
   i::Handle<i::FixedArray> value;
   has_pending_exception =
       !i::JSReceiver::GetKeys(self, i::OWN_ONLY, i::ENUMERABLE_STRINGS)
            .ToHandle(&value);
   RETURN_ON_FAILED_EXECUTION(Array);
-  // Because we use caching to speed up enumeration it is important
-  // to never change the result of the basic enumeration function so
-  // we clone the result.
-  auto elms = isolate->factory()->CopyFixedArray(value);
-  auto result = isolate->factory()->NewJSArrayWithElements(elms);
+  DCHECK(self->map()->EnumLength() == i::kInvalidEnumCacheSentinel ||
+         self->map()->EnumLength() == 0 ||
+         self->map()->instance_descriptors()->GetEnumCache() != *value);
+  auto result = isolate->factory()->NewJSArrayWithElements(value);
   RETURN_ESCAPED(Utils::ToLocal(result));
 }
 
 
 Local<Array> v8::Object::GetOwnPropertyNames() {
   auto context = ContextFromHeapObject(Utils::OpenHandle(this));
   RETURN_TO_LOCAL_UNCHECKED(GetOwnPropertyNames(context), Array);
 }
 
 
@@ skipping 4812 matching lines @@
   Address callback_address =
       reinterpret_cast<Address>(reinterpret_cast<intptr_t>(callback));
   VMState<EXTERNAL> state(isolate);
   ExternalCallbackScope call_scope(isolate, callback_address);
   callback(info);
 }
 
 
 }  // namespace internal
 }  // namespace v8