Use specific messages for const constructor with body.

pkg/compiler/lib/src/tree/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 tree;
 
 abstract class Visitor<R> {
   const Visitor();
 
   R visitNode(Node node);
@@ skipping 822 matching lines @@
   visitChildren(Visitor visitor) {
     if (modifiers != null) modifiers.accept(visitor);
     if (returnType != null) returnType.accept(visitor);
     if (name != null) name.accept(visitor);
     if (parameters != null) parameters.accept(visitor);
     if (initializers != null) initializers.accept(visitor);
     if (asyncModifier != null) asyncModifier.accept(visitor);
     if (body != null) body.accept(visitor);
   }
 
-  bool hasBody() => body.asEmptyStatement() == null;
+  bool get hasBody => body.asEmptyStatement() == null;
 
-  bool hasEmptyBody() {
+  bool get hasEmptyBody {
     Block block = body.asBlock();
     if (block == null) return false;
     return block.statements.isEmpty;
   }
 
   Token getBeginToken() {
     Token token = firstBeginToken(modifiers, returnType);
     if (token != null) return token;
     if (getOrSet != null) return getOrSet;
     return firstBeginToken(name, parameters);
@@ skipping 1625 matching lines @@
 
   // VariableDefinitions.
   get metadata => null;
   get type => null;
 
   // Typedef.
   get typeParameters => null;
   get formals => null;
   get typedefKeyword => null;
 }