[es6] Fix tail call elimination in single-expression arrow functions.

src/parsing/parser.cc

Index: src/parsing/parser.cc
diff --git a/src/parsing/parser.cc b/src/parsing/parser.cc
index 15792805e452175a1efe9e27950f69bf1aa114a8..61aa721d9a82f00915b78d6345827cc29c72863e 100644
--- a/src/parsing/parser.cc
+++ b/src/parsing/parser.cc
@@ -762,6 +762,9 @@ ClassLiteral* ParserTraits::ParseClassLiteral(
                                     name_is_strict_reserved, pos, ok);
 }
 
+void ParserTraits::MarkTailPosition(Expression* expression) {
+  expression->MarkTail();
+}
 
 Parser::Parser(ParseInfo* info)
     : ParserBase<ParserTraits>(info->zone(), &scanner_, info->stack_limit(),
@@ -4578,7 +4581,7 @@ ZoneList<Statement*>* Parser::ParseEagerFunctionBody(
   const List<Expression*>& expressions_in_tail_position =
       function_state_->expressions_in_tail_position();
   for (int i = 0; i < expressions_in_tail_position.length(); ++i) {
-    expressions_in_tail_position[i]->MarkTail();
+    MarkTailPosition(expressions_in_tail_position[i]);
   }
   return result;
 }