[builtins] FastNewClosureStub becomes a builtin.

src/contexts.h

Index: src/contexts.h
diff --git a/src/contexts.h b/src/contexts.h
index 5d4c8ac1647ac63f862637e7afee918e0d97a621..37fb4360c3208b9649b01c270c3ac6d98a6a0181 100644
--- a/src/contexts.h
+++ b/src/contexts.h
@@ -638,7 +638,7 @@ class Context: public FixedArray {
   }
 
   static int FunctionMapIndex(LanguageMode language_mode, FunctionKind kind) {
-    // Note: Must be kept in sync with FastNewClosureStub::Generate.
+    // Note: Must be kept in sync with the FastNewClosure builtin.
     if (IsGeneratorFunction(kind)) {
       return is_strict(language_mode) ? STRICT_GENERATOR_FUNCTION_MAP_INDEX
                                       : SLOPPY_GENERATOR_FUNCTION_MAP_INDEX;