[json] handle proxies in BasicJsonSerializer.

src/builtins.cc

Index: src/builtins.cc
diff --git a/src/builtins.cc b/src/builtins.cc
index d869fd0961b1413f4843f4cb8c0787dbb419fb45..30ec45199aa0a8bcc6465b251ceeff746003672a 100644
--- a/src/builtins.cc
+++ b/src/builtins.cc
@@ -1088,12 +1088,8 @@ bool IterateElements(Isolate* isolate, Handle<JSReceiver> receiver,
     length = static_cast<uint32_t>(array->length()->Number());
   } else {
     Handle<Object> val;
-    Handle<Object> key = isolate->factory()->length_string();
     ASSIGN_RETURN_ON_EXCEPTION_VALUE(
-        isolate, val, Runtime::GetObjectProperty(isolate, receiver, key),
-        false);
-    ASSIGN_RETURN_ON_EXCEPTION_VALUE(isolate, val,
-                                     Object::ToLength(isolate, val), false);
+        isolate, val, Object::GetLengthFromArrayLike(isolate, receiver), false);
     // TODO(caitp): Support larger element indexes (up to 2^53-1).
     if (!val->ToUint32(&length)) {
       length = 0;