Report errors when factory redirection is used in non-factory methods.

dart/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;
 
 class MessageKind {
   final String template;
   const MessageKind(this.template);
 
@@ skipping 317 matching lines @@
 
   static const WRONG_NUMBER_OF_ARGUMENTS_FOR_ASSERT = const MessageKind(
       "Wrong number of arguments to assert. Should be 1, but given #{1}.");
 
   static const ASSERT_IS_GIVEN_NAMED_ARGUMENTS = const MessageKind(
       "assert takes no named arguments, but given #{1}.");
 
   static const MALFORMED_TYPE_REFERENCE = const MessageKind(
       "Malformed type reference encountered in #{1}.");
 
+  static const FACTORY_REDIRECTION_IN_NON_FACTORY = const MessageKind(
+      "Error: Factory redirection only allowed in factories.");
+
+  static const MISSING_FACTORY_KEYWORD = const MessageKind(
+      "Did you forget a factory keyword here?");
+
   static const COMPILER_CRASHED = const MessageKind(
       "Error: The compiler crashed when compiling this element.");
 
   static const PLEASE_REPORT_THE_CRASH = const MessageKind('''
 The compiler is broken.
 
 When compiling the above element, the compiler crashed. It is not
 possible to tell if this is caused by a problem in your program or
 not. Regardless, the compiler should not crash.
 
@@ skipping 78 matching lines @@
 
 class CompileTimeConstantError extends Diagnostic {
   CompileTimeConstantError(MessageKind kind, List arguments)
     : super(kind, arguments);
 }
 
 class CompilationError extends Diagnostic {
   CompilationError(MessageKind kind, List arguments)
     : super(kind, arguments);
 }