fix readability regressions from previous block-scope CL

lib/src/js/nodes.dart

 // Copyright (c) 2012, 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.
 
 part of js_ast;
 
 abstract class NodeVisitor<T> {
   T visitProgram(Program node);
 
   T visitBlock(Block node);
@@ skipping 267 matching lines @@
 
 class Block extends Statement {
   final List<Statement> statements;
 
   /// True to preserve this [Block] for scoping reasons.
   final bool isScope;
 
   Block(this.statements, {this.isScope: false}) {
     assert(!statements.any((s) => s is! Statement));
   }
-  Block.empty() : this.statements = <Statement>[];
+  Block.empty() : statements = <Statement>[], isScope = false;
 
   accept(NodeVisitor visitor) => visitor.visitBlock(this);
   void visitChildren(NodeVisitor visitor) {
     for (Statement statement in statements) statement.accept(visitor);
   }
   Block _clone() => new Block(statements);
 }
 
 class ExpressionStatement extends Statement {
   final Expression expression;
@@ skipping 1268 matching lines @@
   final Expression expression;
 
   CommentExpression(this.comment, this.expression);
 
   int get precedenceLevel => PRIMARY;
   accept(NodeVisitor visitor) => visitor.visitCommentExpression(this);
   CommentExpression _clone() => new CommentExpression(comment, expression);
 
   void visitChildren(NodeVisitor visitor) => expression.accept(visitor);
 }