Use specific messages for const constructor with body.

pkg/compiler/lib/src/resolution/constructors.dart

 // Copyright (c) 2015, 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.
 
 library dart2js.resolution.constructors;
 
 import '../common.dart';
 import '../common/resolution.dart' show
     Feature;
 import '../compiler.dart' show
@@ skipping 388 matching lines @@
               constructorInvocation = result.constant;
             } else {
               isValidAsConstant = false;
             }
           }
           resolvedSuper = true;
         } else if (Initializers.isConstructorRedirect(call)) {
           // Check that there is no body (Language specification 7.5.1).  If the
           // constructor is also const, we already reported an error in
           // [resolveMethodElement].
-          if (functionNode.hasBody() && !constructor.isConst) {
+          if (functionNode.hasBody && !constructor.isConst) {
             reporter.reportErrorMessage(
                 functionNode, MessageKind.REDIRECTING_CONSTRUCTOR_HAS_BODY);
           }
           // Check that there are no other initializers.
           if (!initializers.tail.isEmpty) {
             reporter.reportErrorMessage(
                 call, MessageKind.REDIRECTING_CONSTRUCTOR_HAS_INITIALIZER);
           } else {
             constructor.isRedirectingGenerative = true;
           }
@@ skipping 451 matching lines @@
     // constructors.
     return null;
   }
   // TODO(johnniwinther): Use [Name] for lookup.
   ConstructorElement constructor = cls.lookupConstructor(constructorName);
   if (constructor != null) {
     constructor = constructor.declaration;
   }
   return constructor;
 }