Use specific messages for const constructor with body.

tests/compiler/dart2js/patch_test.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.
 
 import 'dart:async';
 import 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/diagnostics/messages.dart' show
     MessageKind;
@@ skipping 39 matching lines @@
     Expect.isNotNull(node.body);
     // If the element has a body it is either a Block or a Return statement,
     // both with different begin and end tokens.
     Expect.isTrue(node.body is Block || node.body is Return);
     Expect.notEquals(node.body.getBeginToken(), node.body.getEndToken());
 }
 
 void expectHasNoBody(compiler, ElementX element) {
     var node = element.parseNode(compiler.parsing);
     Expect.isNotNull(node, "Element isn't parseable, when a body was expected");
-    Expect.isFalse(node.hasBody());
+    Expect.isFalse(node.hasBody);
 }
 
 Element ensure(compiler,
                String name,
                Element lookup(name),
                {bool expectIsPatched: false,
                 bool expectIsPatch: false,
                 bool checkHasBody: false,
                 bool expectIsGetter: false,
                 bool expectIsFound: true,
@@ skipping 1039 matching lines @@
     await testPatchNonFunction();
 
     await testPatchAndSelector();
 
     await testEffectiveTarget();
 
     await testAnalyzeAllInjectedMembers();
     await testTypecheckPatchedMembers();
   });
 }