[es6] parse arrow ConciseBody with accept_IN flag

src/parser.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/parser.h"
 
 #include "src/api.h"
 #include "src/ast.h"
 #include "src/ast-literal-reindexer.h"
 #include "src/bailout-reason.h"
@@ skipping 1199 matching lines @@
           ParseFormalParameter(&formals, &formals_classifier, &ok);
           if (ok) {
             DeclareFormalParameter(formals.scope, formals.at(0),
                                    &formals_classifier);
           }
         }
       }
 
       if (ok) {
         checkpoint.Restore(&formals.materialized_literals_count);
+        // Pass `accept_IN=true` to ParseArrowFunctionLiteral --- This should
+        // not be observable, or else the preparser would have failed.
         Expression* expression =
-            ParseArrowFunctionLiteral(formals, formals_classifier, &ok);
+            ParseArrowFunctionLiteral(true, formals, formals_classifier, &ok);
         if (ok) {
           // Scanning must end at the same position that was recorded
           // previously. If not, parsing has been interrupted due to a stack
           // overflow, at which point the partially parsed arrow function
           // concise body happens to be a valid expression. This is a problem
           // only for arrow functions with single expression bodies, since there
           // is no end token such as "}" for normal functions.
           if (scanner()->location().end_pos == shared_info->end_position()) {
             // The pre-parser saw an arrow function here, so the full parser
             // must produce a FunctionLiteral.
@@ skipping 5105 matching lines @@
 
 Expression* Parser::SpreadCallNew(Expression* function,
                                   ZoneList<v8::internal::Expression*>* args,
                                   int pos) {
   args->InsertAt(0, function, zone());
 
   return factory()->NewCallRuntime(Context::REFLECT_CONSTRUCT_INDEX, args, pos);
 }
 }  // namespace internal
 }  // namespace v8