[es6] Re-implement rest parameters via desugaring.

src/ast-literal-reindexer.h

 // Copyright 2015 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_AST_LITERAL_REINDEXER
 #define V8_AST_LITERAL_REINDEXER
 
 #include "src/ast.h"
 #include "src/scopes.h"
 
 namespace v8 {
 namespace internal {
 
 class AstLiteralReindexer final : public AstVisitor {
  public:
   AstLiteralReindexer() : AstVisitor(), next_index_(0) {}
 
   int count() const { return next_index_; }
   void Reindex(Expression* pattern);
+  int NextIndex() { return next_index_++; }
 
  private:
 #define DEFINE_VISIT(type) virtual void Visit##type(type* node) override;
   AST_NODE_LIST(DEFINE_VISIT)
 #undef DEFINE_VISIT
 
   void VisitStatements(ZoneList<Statement*>* statements) override;
   void VisitDeclarations(ZoneList<Declaration*>* declarations) override;
   void VisitArguments(ZoneList<Expression*>* arguments);
   void VisitObjectLiteralProperty(ObjectLiteralProperty* property);
 
   void UpdateIndex(MaterializedLiteral* literal) {
     literal->literal_index_ = next_index_++;
   }
 
   void Visit(AstNode* node) override { node->Accept(this); }
 
   int next_index_;
 
   DISALLOW_COPY_AND_ASSIGN(AstLiteralReindexer);
 };
 }
 }  // namespace v8::internal
 
 #endif  // V8_AST_LITERAL_REINDEXER