anchor.diff:      ..add(ifKeyword)
       ..add(leftParenthesis)
       ..add(_condition)
  -    ..add(rightParenthesis)
  -    ..add(elseKeyword);
  +    ..add(rightParenthesis);
   
     Expression get condition => _condition;
   
  
positive.code:   Iterable<SyntacticEntity> get childEntities => new ChildEntities()
      ..addAll(super.childEntities)
      ..add(_thenElement)
      ..add(_elseElement);
  
    @override
  
negative.code: ///
  ///    ifStatement ::=
  ///        'if' '(' [Expression] ')' [Statement] ('else' [Statement])?
  class IfStatementImpl extends StatementImpl
      with IfMixin
      implements IfStatement {
    /// The statement that is executed if the condition evaluates to `true`.
    StatementImpl _thenStatement;
  
    /// The statement that is executed if the condition evaluates to `false`, or
    /// `null` if there is no else statement.
  