Parse parenthesized expressions.

dart/frog/leg/tree/visitors.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class AbstractVisitor<R> implements Visitor<R> {
   abstract R visitNode(Node node);
 
   R visitBlock(Block node) => visitStatement(node);
   R visitClassNode(ClassNode node) => visitNode(node);
   R visitDoWhile(DoWhile node) => visitLoop(node);
   R visitExpression(Expression node) => visitNode(node);
   R visitExpressionStatement(ExpressionStatement node) => visitStatement(node);
   R visitFor(For node) => visitStatement(node);
   R visitFunctionExpression(FunctionExpression node) => visitExpression(node);
   R visitIdentifier(Identifier node) => visitExpression(node);
   R visitIf(If node) => visitStatement(node);
   R visitLiteral(Literal node) => visitExpression(node);
   R visitLiteralBool(LiteralBool node) => visitLiteral(node);
   R visitLiteralDouble(LiteralDouble node) => visitLiteral(node);
   R visitLiteralInt(LiteralInt node) => visitLiteral(node);
   R visitLiteralNull(LiteralNull node) => visitLiteral(node);
   R visitLiteralString(LiteralString node) => visitLiteral(node);
   R visitLoop(Loop node) => visitStatement(node);
   R visitNewExpression(NewExpression node) => visitExpression(node);
   R visitNodeList(NodeList node) => visitNode(node);
   R visitOperator(Operator node) => visitIdentifier(node);
+  R visitParenthesizedExpression(ParenthesizedExpression node) {
+    return visitExpression(node);
+  }
   R visitPostfix(Postfix node) => visitNodeList(node);
   R visitPrefix(Prefix node) => visitNodeList(node);
   R visitReturn(Return node) => visitStatement(node);
   R visitSend(Send node) => visitExpression(node);
   R visitSendSet(SendSet node) => visitSend(node);
   R visitStatement(Statement node) => visitNode(node);
   R visitThrow(Throw node) => visitStatement(node);
   R visitTypeAnnotation(TypeAnnotation node) => visitNode(node);
   R visitVariableDefinitions(VariableDefinitions node) => visitStatement(node);
   R visitWhile(While node) => visitLoop(node);
 }