Disable ES6 tail call elimination for native functions.

src/parsing/parser.cc

Index: src/parsing/parser.cc
diff --git a/src/parsing/parser.cc b/src/parsing/parser.cc
index 3bc11bea9058cf9fccc392d5a4d66e9692deb9cb..12e746cd12b16b0ed36546239285ea61f994152e 100644
--- a/src/parsing/parser.cc
+++ b/src/parsing/parser.cc
@@ -783,6 +783,7 @@ Parser::Parser(ParseInfo* info)
   DCHECK(!info->script().is_null() || info->source_stream() != NULL);
   set_allow_lazy(info->allow_lazy_parsing());
   set_allow_natives(FLAG_allow_natives_syntax || info->is_native());
+  set_allow_tailcalls(FLAG_harmony_tailcalls && !info->is_native());
   set_allow_harmony_sloppy(FLAG_harmony_sloppy);
   set_allow_harmony_sloppy_function(FLAG_harmony_sloppy_function);
   set_allow_harmony_sloppy_let(FLAG_harmony_sloppy_let);
@@ -2680,7 +2681,7 @@ Statement* Parser::ParseReturnStatement(bool* ok) {
     }
 
     // ES6 14.6.1 Static Semantics: IsInTailPosition
-    if (FLAG_harmony_tailcalls && !is_sloppy(language_mode())) {
+    if (allow_tailcalls() && !is_sloppy(language_mode())) {
       function_state_->AddExpressionInTailPosition(return_value);
     }
   }