[es6] support rest parameters in arrow functions (alternative)

test/cctest/test-parsing.cc

 // Copyright 2012 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 4810 matching lines @@
                     arraysize(always_flags));
 }
 
 
 TEST(ParseRestParameters) {
   const char* context_data[][2] = {{"'use strict';(function(",
                                     "){ return args;})(1, [], /regexp/, 'str',"
                                     "function(){});"},
                                    {"(function(", "){ return args;})(1, [],"
                                     "/regexp/, 'str', function(){});"},
+                                   {"((", ") => args)(1, [], /regexp/, 'str',"
+                                    "function(){});"},
                                   {NULL, NULL}};
 
   const char* data[] = {
     "...args",
     "a, ...args",
     "...   args",
     "a, ...   args",
     "...\targs",
     "a, ...\targs",
     "...\r\nargs",
     "a, ...\r\nargs",
     "...\rargs",
     "a, ...\rargs",
     "...\t\n\t\t\n  args",
     "a, ...  \n  \n  args",
     NULL};
-  static const ParserFlag always_flags[] = {kAllowHarmonyRestParameters};
+  static const ParserFlag always_flags[] =
+      {kAllowHarmonyRestParameters, kAllowHarmonyArrowFunctions};
   RunParserSyncTest(context_data, data, kSuccess, NULL, 0, always_flags,
                     arraysize(always_flags));
 }
 
 
 TEST(ParseRestParametersErrors) {
   const char* context_data[][2] = {{"'use strict';(function(",
                                     "){ return args;}(1, [], /regexp/, 'str',"
                                     "function(){});"},
                                    {"(function(", "){ return args;}(1, [],"
@@ skipping 717 matching lines @@
       "(a/*\n*/=> a)(1)",
       "((a)\n=> a)(1)",
       "((a)/*\n*/=> a)(1)",
       "((a, b)\n=> a + b)(1, 2)",
       "((a, b)/*\n*/=> a + b)(1, 2)",
       NULL};
   static const ParserFlag always_flags[] = {kAllowHarmonyArrowFunctions};
   RunParserSyncTest(context_data, data, kError, NULL, 0, always_flags,
                     arraysize(always_flags));
 }