[es6] implement default/optional parameters (WIP / comments)

src/ast-value-factory.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 153 matching lines @@
   bool EqualsString(const AstRawString* string) const {
     return type_ == STRING && string_ == string;
   }
 
   bool IsPropertyName() const;
 
   bool BooleanValue() const;
 
   void Internalize(Isolate* isolate);
 
+  bool IsUndefined() const {
+    return type_ == UNDEFINED;
+  }
+
   // Can be called after Internalize has been called.
   V8_INLINE Handle<Object> value() const {
     if (type_ == STRING) {
       return string_->string();
     }
     DCHECK(!value_.is_null());
     return value_;
   }
 
  private:
@@ skipping 179 matching lines @@
 #define F(name) AstValue* name##_;
   OTHER_CONSTANTS(F)
 #undef F
 };
 } }  // namespace v8::internal
 
 #undef STRING_CONSTANTS
 #undef OTHER_CONSTANTS
 
 #endif  // V8_AST_VALUE_FACTORY_H_