Use shared error for constructor's with return type.

pkg/compiler/lib/src/diagnostics/generated/shared_messages.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.
 /*
 DON'T EDIT. GENERATED. DON'T EDIT.
 This file has been generated by 'publish.dart' in the dart_messages package.
 
 Messages are maintained in `lib/shared_messages.dart` of that same package.
 After any change to that file, run `bin/publish.dart` to generate a new version
 of the json, dart2js and analyzer representations.
@@ skipping 47 matching lines @@
     MessageKind.EXTRANEOUS_MODIFIER_REPLACE,
     "Can't have modifier '#{modifier}' here.",
     howToFix: "Try replacing modifier '#{modifier}' with 'var', 'final', or a type.",
     examples: const [
       "set foo; main(){}",
       "abstract foo; main(){}",
       "static foo; main(){}",
       "external foo; main(){}",
     ]
   ),  // Generated. Don't edit.
+  MessageKind.CONSTRUCTOR_WITH_RETURN_TYPE: const MessageTemplate(
+    MessageKind.CONSTRUCTOR_WITH_RETURN_TYPE,
+    "Constructors can't have a return type",
+    howToFix: "Try removing the return type.",
+    examples: const [
+      "class A { int A() {} } main() { new A(); }",
+    ]
+  ),  // Generated. Don't edit.
 };