Follow factory redirections when checking case expressions.

sdk/lib/_internal/compiler/implementation/warnings.dart

 // Copyright (c) 2011, 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 dart2js;
 
 const DONT_KNOW_HOW_TO_FIX = "";
 
 /**
  * The messages in this file should meet the following guide lines:
@@ skipping 522 matching lines @@
 
   static const MessageKind INVALID_CASE_DEFAULT = const MessageKind(
       "'default' only allowed on last case of a switch.");
 
   static const MessageKind SWITCH_CASE_TYPES_NOT_EQUAL = const MessageKind(
       "'case' expressions do not all have type '#{type}'.");
 
   static const MessageKind SWITCH_CASE_TYPES_NOT_EQUAL_CASE = const MessageKind(
       "'case' expression of type '#{type}'.");
 
+  static const MessageKind SWITCH_CASE_FORBIDDEN = const MessageKind(
+      "'case' expression may not be of type '#{type}'.");
+
   static const MessageKind SWITCH_CASE_VALUE_OVERRIDES_EQUALS =
       const MessageKind(
           "'case' expression type '#{type}' overrides 'operator =='.");
 
   static const MessageKind INVALID_ARGUMENT_AFTER_NAMED = const MessageKind(
       "Unnamed argument after named argument.");
 
   static const MessageKind NOT_A_COMPILE_TIME_CONSTANT = const MessageKind(
       "Not a compile-time constant.");
 
@@ skipping 1338 matching lines @@
     return computeMessage();
   }
 
   bool operator==(other) {
     if (other is !Message) return false;
     return (kind == other.kind) && (toString() == other.toString());
   }
 
   int get hashCode => throw new UnsupportedError('Message.hashCode');
 }