[runtime] Rewrite Function.prototype.toString in C++.

src/js/prologue.js

 // Copyright 2015 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.
 
 (function(global, utils, extrasUtils) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
@@ skipping 153 matching lines @@
   %CheckIsBootstrapping();
 
   for ( ; !IS_UNDEFINED(imports); imports = imports.next) {
     imports(exports_container);
   }
 
   // Whitelist of exports from normal natives to experimental natives and debug.
   var expose_list = [
     "ArrayToString",
     "ErrorToString",
-    "FunctionSourceString",
     "GetIterator",
     "GetMethod",
     "InnerArrayEvery",
     "InnerArrayFilter",
     "InnerArrayForEach",
     "InnerArrayIndexOf",
     "InnerArrayJoin",
     "InnerArrayLastIndexOf",
     "InnerArrayMap",
     "InnerArrayReduce",
@@ skipping 159 matching lines @@
 
 extrasUtils.uncurryThis = function uncurryThis(func) {
   return function(thisArg) {
     return %Apply(func, thisArg, arguments, 1, arguments.length - 1);
   };
 };
 
 %ToFastProperties(extrasUtils);
 
 })