[es6] Re-implement rest parameters via desugaring.

src/parser.h

 // 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.
 
 #ifndef V8_PARSER_H_
 #define V8_PARSER_H_
 
 #include "src/allocation.h"
 #include "src/ast.h"
 #include "src/compiler.h"  // TODO(titzer): remove this include dependency
@@ skipping 1320 matching lines @@
       ParserFormalParameters::Parameter(name, pattern, initializer, is_rest),
       parameters->scope->zone());
 }
 
 
 void ParserTraits::DeclareFormalParameter(
     Scope* scope, const ParserFormalParameters::Parameter& parameter,
     ExpressionClassifier* classifier) {
   bool is_duplicate = false;
   bool is_simple = classifier->is_simple_parameter_list();
-  // TODO(caitp): Remove special handling for rest once desugaring is in.
-  auto name = is_simple || parameter.is_rest
-      ? parameter.name : parser_->ast_value_factory()->empty_string();
-  auto mode = is_simple || parameter.is_rest ? VAR : TEMPORARY;
+  auto name = parameter.name;
+  auto mode = is_simple ? VAR : TEMPORARY;
   if (!is_simple) scope->SetHasNonSimpleParameters();
   bool is_optional = parameter.initializer != nullptr;
   Variable* var = scope->DeclareParameter(
       name, mode, is_optional, parameter.is_rest, &is_duplicate);
   if (is_duplicate) {
     classifier->RecordDuplicateFormalParameterError(
         parser_->scanner()->location());
   }
   if (is_sloppy(scope->language_mode())) {
     // TODO(sigurds) Mark every parameter as maybe assigned. This is a
@@ skipping 12 matching lines @@
         parser_->BuildParameterInitializationBlock(parameters, ok);
     if (!*ok) return;
     if (init_block != nullptr) {
       body->Add(init_block, parser_->zone());
     }
   }
 }
 } }  // namespace v8::internal
 
 #endif  // V8_PARSER_H_