Fix for-in for large indexes and indexes on proxies

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 33aa523d55006e371708bc41e55a57ab8c1cddfe..4b7341ece9f02d2e7f1aa0886c2a67cfc47f1f1c 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1107,6 +1107,11 @@ class Object {
     return true;
   }
 
+  // Checks whether two valid primitive encodings of a property name resolve to
+  // the same logical property. E.g., the smi 1, the string "1" and the double
+  // 1 all refer to the same property, so this helper will return true.
+  inline bool KeyEquals(Object* other);
+
   Handle<HeapType> OptimalType(Isolate* isolate, Representation representation);
 
   inline static Handle<Object> NewStorageFor(Isolate* isolate,