Improve message for import of part.

pkg/compiler/lib/src/elements/modelx.dart

 // Copyright (c) 2013, 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 elements.modelx;
 
 import 'elements.dart';
 import '../constants/expressions.dart';
 import '../helpers/helpers.dart';  // Included for debug helpers.
 import '../tree/tree.dart';
@@ skipping 545 matching lines @@
     if (enclosingElement.isPatch) {
       implementationLibrary.addMember(element, listener);
     } else {
       library.addMember(element, listener);
     }
   }
 
   void setPartOf(PartOf tag, DiagnosticListener listener) {
     LibraryElementX library = enclosingElement;
     if (library.entryCompilationUnit == this) {
-      listener.reportError(tag, MessageKind.ILLEGAL_DIRECTIVE);
+      listener.reportError(tag, MessageKind.IMPORT_PART_OF);
       return;
     }
     if (!localMembers.isEmpty) {
       listener.reportError(tag, MessageKind.BEFORE_TOP_LEVEL);
       return;
     }
     if (partTag != null) {
       listener.reportWarning(tag, MessageKind.DUPLICATED_PART_OF);
       return;
     }
@@ skipping 2248 matching lines @@
   AstElement get definingElement;
 
   bool get hasResolvedAst => definingElement.hasTreeElements;
 
   ResolvedAst get resolvedAst {
     return new ResolvedAst(declaration,
         definingElement.node, definingElement.treeElements);
   }
 
 }