[builtins] Migrate String.fromCharCode to C++.

test/mjsunit/string-fromcharcode.js

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 85 matching lines @@
   assertEquals(expected, fcc2(0x20));
   assertEquals(expected, fcc2(0x20 - 0x10000));
   assertEquals(expected, fcc2(0x20 + 0.5));
 }
 
 // Use loop to test the custom IC.
 for (var i = 0; i < 10; i++) {
   test(i);
 }
 
-assertEquals("AAAA", String.fromCharCode(65, 65, 65, 65));
-assertEquals("AAAA", String.fromCharCode(65, 65, 65, 65));
-%OptimizeFunctionOnNextCall(String.fromCharCode);
-assertEquals("AAAA", String.fromCharCode(65, 65, 65, 65));
-
 // Test the custom IC works correctly when the map changes.
 for (var i = 0; i < 10; i++) {
   var expected = (i < 5) ? " " : 42;
   if (i == 5) String.fromCharCode = function() { return 42; };
   assertEquals(expected, String.fromCharCode(0x20));
 }