[runtime] Replace %to_string_fun with %_ToString.

src/runtime/runtime-json.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/char-predicates-inl.h"
 #include "src/isolate-inl.h"
 #include "src/json-parser.h"
@@ skipping 21 matching lines @@
   BasicJsonStringifier stringifier(isolate);
   Handle<Object> result;
   ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, result,
                                      stringifier.Stringify(object));
   return *result;
 }
 
 
 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;
   ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, result,
                                      source->IsSeqOneByteString()
                                          ? JsonParser<true>::Parse(source)
                                          : JsonParser<false>::Parse(source));
   return *result;
 }
+
 }  // namespace internal
 }  // namespace v8