[json] handle proxies in BasicJsonSerializer.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index acc4b84c609ed15751ca833384027b546e442f1c..8cc551f508bf8635bfd68af77df23de345b1c113 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1177,6 +1177,10 @@ class Object {
   MUST_USE_RESULT static MaybeHandle<FixedArray> CreateListFromArrayLike(
       Isolate* isolate, Handle<Object> object, ElementTypes element_types);
 
+  // Get length property and apply ToLength.
+  MUST_USE_RESULT static MaybeHandle<Object> GetLengthFromArrayLike(
+      Isolate* isolate, Handle<Object> object);
+
   // Check whether |object| is an instance of Error or NativeError.
   static bool IsErrorObject(Isolate* isolate, Handle<Object> object);