Implement cascaded calls.

lib/compiler/implementation/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> {
   const AbstractVisitor();
 
   abstract R visitNode(Node node);
 
   R visitBlock(Block node) => visitStatement(node);
   R visitBreakStatement(BreakStatement node) => visitGotoStatement(node);
+  R visitCascade(Cascade node) => visitExpression(node);
+  R visitCascadeReceiver(CascadeReceiver node) => visitExpression(node);
   R visitCatchBlock(CatchBlock node) => visitNode(node);
   R visitClassNode(ClassNode node) => visitNode(node);
   R visitConditional(Conditional node) => visitExpression(node);
   R visitContinueStatement(ContinueStatement node) => visitGotoStatement(node);
   R visitDoWhile(DoWhile node) => visitLoop(node);
   R visitEmptyStatement(EmptyStatement node) => visitStatement(node);
   R visitExpression(Expression node) => visitNode(node);
   R visitExpressionStatement(ExpressionStatement node) => visitStatement(node);
   R visitFor(For node) => visitLoop(node);
   R visitForIn(ForIn node) => visitLoop(node);
@@ skipping 53 matching lines @@
 class TraversingVisitor extends AbstractVisitor {
   final Visitor visitor;
 
   TraversingVisitor(Visitor this.visitor);
 
   visitNode(Node node) {
     node.accept(visitor);
     node.visitChildren(this);
   }
 }