Fix bad example of URI part-of to be bad, not good.

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 2075 matching lines @@
           examples: const [
             const {
               'main.dart': """
 library lib.foo;
 
 part 'part.dart';
 
 main() {}
 """,
               'part.dart': """
-part of "main.dart";
+part of 'not-main.dart';
 """
             }
           ]),
 
       MessageKind.MISSING_LIBRARY_NAME: const MessageTemplate(
           MessageKind.MISSING_LIBRARY_NAME,
           "Library has no name. Part directive expected library name "
           "to be '#{libraryName}'.",
           howToFix: "Try adding 'library #{libraryName};' to the library.",
           examples: const [
@@ skipping 1732 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';
   }
 }