[runtime] Replace %to_string_fun with %_ToString.

src/runtime/runtime-json.cc

Index: src/runtime/runtime-json.cc
diff --git a/src/runtime/runtime-json.cc b/src/runtime/runtime-json.cc
index 07ccb9938fb5149850554d5ab1aebc2dfc300651..07232d59b8ba66c59d4d315dea0315f62bc9230a 100644
--- a/src/runtime/runtime-json.cc
+++ b/src/runtime/runtime-json.cc
@@ -39,9 +39,11 @@ RUNTIME_FUNCTION(Runtime_BasicJSONStringify) {
 
 RUNTIME_FUNCTION(Runtime_ParseJson) {
   HandleScope scope(isolate);
-  DCHECK(args.length() == 1);
-  CONVERT_ARG_HANDLE_CHECKED(String, source, 0);
-
+  DCHECK_EQ(1, args.length());
+  CONVERT_ARG_HANDLE_CHECKED(Object, object, 0);
+  Handle<String> source;
+  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, source,
+                                     Object::ToString(isolate, object));
   source = String::Flatten(source);
   // Optimized fast case where we only have Latin1 characters.
   Handle<Object> result;
@@ -51,5 +53,6 @@ RUNTIME_FUNCTION(Runtime_ParseJson) {
                                          : JsonParser<false>::Parse(source));
   return *result;
 }
+
 }  // namespace internal
 }  // namespace v8