[json] replace remaining json.js code with C++ builtins.

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"
-#include "src/json-stringifier.h"
-#include "src/objects-inl.h"
-
-namespace v8 {
-namespace internal {
-
-RUNTIME_FUNCTION(Runtime_ParseJson) {
-  HandleScope scope(isolate);
-  DCHECK_EQ(2, args.length());
-  CONVERT_ARG_HANDLE_CHECKED(Object, object, 0);
-  CONVERT_ARG_HANDLE_CHECKED(Object, reviver, 1);
-  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.
-  RETURN_RESULT_OR_FAILURE(
-      isolate, source->IsSeqOneByteString()
-                   ? JsonParser<true>::Parse(isolate, source, reviver)
-                   : JsonParser<false>::Parse(isolate, source, reviver));
-}
-
-}  // namespace internal
-}  // namespace v8