[es6] Re-implement rest parameters via desugaring.

src/preparser.h

Index: src/preparser.h
diff --git a/src/preparser.h b/src/preparser.h
index d240db1b912955a87b75052b7cf6571b005f494f..938fd3f1620466e90d420d2b34b8a525909b6833 100644
--- a/src/preparser.h
+++ b/src/preparser.h
@@ -33,6 +33,7 @@ struct FormalParametersBase {
   bool has_rest = false;
   bool is_simple = true;
   int materialized_literals_count = 0;
+  int rest_array_literal_index = 0;
 };
 
 
@@ -3654,10 +3655,14 @@ void ParserBase<Traits>::ParseFormalParameter(
     parameters->is_simple = !is_rest && Traits::IsIdentifier(pattern);
   }
   parameters->has_rest = is_rest;
-  if (is_rest && !Traits::IsIdentifier(pattern)) {
-    ReportUnexpectedToken(next);
-    *ok = false;
-    return;
+  if (is_rest) {
+    if (!Traits::IsIdentifier(pattern)) {
+      ReportUnexpectedToken(next);
+      *ok = false;
+      return;
+    }
+    parameters->rest_array_literal_index =
+        function_state_->NextMaterializedLiteralIndex();
   }
   Traits::AddFormalParameter(parameters, pattern, is_rest);
 }