[es6] implement default parameters via desugaring

src/preparser.cc

Index: src/preparser.cc
diff --git a/src/preparser.cc b/src/preparser.cc
index 3dca827c92738d398bb2dd2639d81a19ca082f34..2ac8d8a4618f86046ada28cf44116b86c5430d24 100644
--- a/src/preparser.cc
+++ b/src/preparser.cc
@@ -1035,14 +1035,17 @@ PreParser::Expression PreParser::ParseFunctionLiteral(
   ExpressionClassifier formals_classifier;
 
   bool has_rest = false;
+  bool has_parameter_expressions = false;
+  PreParserExpressionList initializers = NewExpressionList(0, zone());
   Expect(Token::LPAREN, CHECK_OK);
   int start_position = scanner()->location().beg_pos;
   function_scope->set_start_position(start_position);
   int num_parameters;
   {
     DuplicateFinder duplicate_finder(scanner()->unicode_cache());
-    num_parameters = ParseFormalParameterList(&duplicate_finder, &has_rest,
-                                              &formals_classifier, CHECK_OK);
+    num_parameters = ParseFormalParameterList(
+        &duplicate_finder, initializers, &has_parameter_expressions, &has_rest,
+        &formals_classifier, CHECK_OK);
   }
   Expect(Token::RPAREN, CHECK_OK);
   int formals_end_position = scanner()->location().end_pos;