[Code Stubs] Convert FastNewClosureStub to a TurboFanCodeStub.

src/contexts.h

Index: src/contexts.h
diff --git a/src/contexts.h b/src/contexts.h
index df592cee07b2c07d493495cb3b93add2cbdc6297..0a1181a7c70da093a4e842d58910094933d17947 100644
--- a/src/contexts.h
+++ b/src/contexts.h
@@ -526,6 +526,7 @@ class Context: public FixedArray {
   }
 
   static int FunctionMapIndex(LanguageMode language_mode, FunctionKind kind) {
+    // Note: Must be kept in sync with FastNewClosureStub::Generate.
     if (IsGeneratorFunction(kind)) {
       return is_strict(language_mode) ? STRICT_GENERATOR_FUNCTION_MAP_INDEX
                                       : SLOPPY_GENERATOR_FUNCTION_MAP_INDEX;