[es6] implement default 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 731 matching lines @@
   ZoneList<ObjectLiteral::Property*>* NewPropertyList(int size, Zone* zone) {
     return new(zone) ZoneList<ObjectLiteral::Property*>(size, zone);
   }
   ZoneList<v8::internal::Statement*>* NewStatementList(int size, Zone* zone) {
     return new(zone) ZoneList<v8::internal::Statement*>(size, zone);
   }
   V8_INLINE Scope* NewScope(Scope* parent_scope, ScopeType scope_type,
                             FunctionKind kind = kNormalFunction);
 
   bool DeclareFormalParameter(Scope* scope, const AstRawString* name,
-                              bool is_rest) {
+                              bool is_rest, int pos) {
     bool is_duplicate = false;
-    Variable* var = scope->DeclareParameter(name, VAR, is_rest, &is_duplicate);
+    Variable* var =
+        scope->DeclareParameter(name, VAR, is_rest, &is_duplicate, pos);
     if (is_sloppy(scope->language_mode())) {
       // TODO(sigurds) Mark every parameter as maybe assigned. This is a
       // conservative approximation necessary to account for parameters
       // that are assigned via the arguments array.
       var->set_maybe_assigned();
     }
     return is_duplicate;
   }
 
   void DeclareArrowFunctionParameters(Scope* scope, Expression* expr,
@@ skipping 299 matching lines @@
   // Initialize the components of a for-in / for-of statement.
   void InitializeForEachStatement(ForEachStatement* stmt,
                                   Expression* each,
                                   Expression* subject,
                                   Statement* body);
   Statement* DesugarLexicalBindingsInForStatement(
       Scope* inner_scope, bool is_const, ZoneList<const AstRawString*>* names,
       ForStatement* loop, Statement* init, Expression* cond, Statement* next,
       Statement* body, bool* ok);
 
+  ZoneList<Statement*>* DesugarInitializeParameters(
+      Scope* scope, bool hasParameterExpressions,
+      ZoneList<Expression*>* initializers);
+
   FunctionLiteral* ParseFunctionLiteral(
       const AstRawString* name, Scanner::Location function_name_location,
       bool name_is_strict_reserved, FunctionKind kind,
       int function_token_position, FunctionLiteral::FunctionType type,
       FunctionLiteral::ArityRestriction arity_restriction, bool* ok);
 
 
   ClassLiteral* ParseClassLiteral(const AstRawString* name,
                                   Scanner::Location class_name_location,
                                   bool name_is_strict_reserved, int pos,
@@ skipping 187 matching lines @@
 }
 
 
 Expression* ParserTraits::SpreadCallNew(
     Expression* function, ZoneList<v8::internal::Expression*>* args, int pos) {
   return parser_->SpreadCallNew(function, args, pos);
 }
 } }  // namespace v8::internal
 
 #endif  // V8_PARSER_H_