Delete dart_backend from compiler.

pkg/compiler/lib/src/diagnostics/messages.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.
 
 /**
  * The messages in this file should meet the following guide lines:
  *
  * 1. The message should be a complete sentence starting with an uppercase
  * letter, and ending with a period.
  *
@@ skipping 3608 matching lines @@
           "Cannot patch non-function with function patch "
           "'#{functionName}'."),
 
       MessageKind.INJECTED_PUBLIC_MEMBER: const MessageTemplate(
           MessageKind.INJECTED_PUBLIC_MEMBER,
           "Non-patch members in patch libraries must be private."),
 
       MessageKind.EXTERNAL_WITH_BODY: const MessageTemplate(
           MessageKind.EXTERNAL_WITH_BODY,
           "External function '#{functionName}' cannot have a function body.",
-          options: const ["--output-type=dart"],
           howToFix:
               "Try removing the 'external' modifier or the function body.",
           examples: const [
             """
+import 'package:js/js.dart';
+@JS()
 external foo() => 0;
 main() => foo();
 """,
             """
+import 'package:js/js.dart';
+@JS()
 external foo() {}
 main() => foo();
 """
           ]),
 
       //////////////////////////////////////////////////////////////////////////////
       // Patch errors end.
       //////////////////////////////////////////////////////////////////////////////
 
       MessageKind.EXPERIMENTAL_ASSERT_MESSAGE: const MessageTemplate(
@@ skipping 159 matching lines @@
   static String convertToString(value) {
     if (value is ErrorToken) {
       // Shouldn't happen.
       return value.assertionMessage;
     } else if (value is Token) {
       value = value.value;
     }
     return '$value';
   }
 }