Support abstract getters without parameters.

dart/lib/compiler/implementation/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.
 
 interface NodeVisitor<T> {
   T visitProgram(Program node);
 
   T visitBlock(Block node);
   T visitExpressionStatement(ExpressionStatement node);
   T visitEmptyStatement(EmptyStatement node);
@@ skipping 408 matching lines @@
 class LiteralStatement extends Statement {
   final String code;
 
   LiteralStatement(this.code);
 
   accept(NodeVisitor visitor) => visitor.visitLiteralStatement(this);
   void visitChildren(NodeVisitor visitor) { }
 }
 
 abstract class Expression extends Node {
-  abstract int get precedenceLevel();
+  abstract int get precedenceLevel;
 }
 
 class LiteralExpression extends Expression {
   final String template;
   final List<Expression> inputs;
 
   LiteralExpression(this.template) : inputs = const [];
   LiteralExpression.withData(this.template, this.inputs);
 
   accept(NodeVisitor visitor) => visitor.visitLiteralExpression(this);
@@ skipping 390 matching lines @@
   /** Contains the pattern and the flags.*/
   String pattern;
 
   RegExpLiteral(this.pattern);
 
   accept(NodeVisitor visitor) => visitor.visitRegExpLiteral(this);
   void visitChildren(NodeVisitor visitor) {}
 
   int get precedenceLevel => PRIMARY;
 }