[proxies] allow duplicate keys for [[OwnPropertyKeys]] trap.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 5a872857bbab22ebeddbbc1a1212d09631803a06..3b916019e6f053b93ba9afe8641f63b2983d882c 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1785,6 +1785,7 @@ enum AccessorComponent {
 
 enum GetKeysConversion { KEEP_NUMBERS, CONVERT_TO_STRING };
 
+enum KeyCollectionType { OWN_ONLY, INCLUDE_PROTOS };
 
 // JSReceiver includes types on which properties can be defined, i.e.,
 // JSObject and JSProxy.
@@ -1946,12 +1947,10 @@ class JSReceiver: public HeapObject {
   inline static Handle<Smi> GetOrCreateIdentityHash(
       Handle<JSReceiver> object);
 
-  enum KeyCollectionType { OWN_ONLY, INCLUDE_PROTOS };
-
   // ES6 [[OwnPropertyKeys]] (modulo return type)
   MUST_USE_RESULT static MaybeHandle<FixedArray> OwnPropertyKeys(
       Handle<JSReceiver> object) {
-    return GetKeys(object, JSReceiver::OWN_ONLY, ALL_PROPERTIES,
+    return GetKeys(object, KeyCollectionType::OWN_ONLY, ALL_PROPERTIES,
                    CONVERT_TO_STRING);
   }