Don't create navigation regions for not existing sources.

pkg/analyzer/lib/src/generated/engine.dart

 // Copyright (c) 2014, 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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine;
 
 import 'dart:async';
@@ skipping 5804 matching lines @@
    */
   void set logger(Logger logger) {
     this._logger = logger == null ? Logger.NULL : logger;
   }
 
   /**
    * Return the list of supported plugins for processing by clients.
    */
   List<Plugin> get supportedPlugins {
     if (_supportedPlugins == null) {
-      _supportedPlugins = <Plugin>[enginePlugin, commandLinePlugin, optionsPlugin];
+      _supportedPlugins = <Plugin>[
+        enginePlugin,
+        commandLinePlugin,
+        optionsPlugin
+      ];
     }
     return _supportedPlugins;
   }
 
   /**
    * Return the task manager used to manage the tasks used to analyze code.
    */
   TaskManager get taskManager {
     if (_taskManager == null) {
       if (enginePlugin.taskExtensionPoint == null) {
@@ skipping 5964 matching lines @@
     PendingFuture pendingFuture =
         new PendingFuture<T>(_context, source, computeValue);
     if (!pendingFuture.evaluate(sourceEntry)) {
       _context._pendingFutureSources
           .putIfAbsent(source, () => <PendingFuture>[])
           .add(pendingFuture);
     }
     return pendingFuture.future;
   }
 }