JavaScript stubs have access to their calling convention and minor key now.

test/mjsunit/compiler/stubs/floor-stub.js

 // Copyright 2015 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 18 matching lines @@
 
 const kExtraTypeFeedbackMinusZeroSentinel = 1;
 const kFirstSlotExtraTypeFeedbackIndex = 5;
 
 (function(){
   var floorFunc = function() {
     Math.floor(NaN);
   }
   // Execute the function once to make sure it has a type feedback vector.
   floorFunc(5);
+  var stub = builtins.MathFloorStub("MathFloorStub", 0);
   assertTrue(kExtraTypeFeedbackMinusZeroSentinel !==
              %FixedArrayGet(%GetTypeFeedbackVector(floorFunc),
                             kFirstSlotExtraTypeFeedbackIndex));
-  assertEquals(5.0, builtins.MathFloor_STUB(floorFunc, 4, 5.5));
+  assertEquals(5.0, stub(floorFunc, 4, 5.5));
   assertTrue(kExtraTypeFeedbackMinusZeroSentinel !==
              %FixedArrayGet(%GetTypeFeedbackVector(floorFunc),
                             kFirstSlotExtraTypeFeedbackIndex));
   // Executing floor such that it returns -0 should set the proper sentinel in
   // the feedback vector.
-  assertEquals(-Infinity, 1/builtins.MathFloor_STUB(floorFunc, 4, -0));
+  assertEquals(-Infinity, 1/stub(floorFunc, 4, -0));
   assertEquals(kExtraTypeFeedbackMinusZeroSentinel,
                %FixedArrayGet(%GetTypeFeedbackVector(floorFunc),
                               kFirstSlotExtraTypeFeedbackIndex));
   %ClearFunctionTypeFeedback(floorFunc);
 })();