Fix for subscribing for notifications for files in packages.

pkg/analysis_server/lib/src/context_manager.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.
 
 library context.directory.manager;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analysis_server/src/analysis_server.dart';
@@ skipping 594 matching lines @@
    * Create and return a source representing the given [file] within the given
    * [context].
    */
   static Source createSourceInContext(AnalysisContext context, File file) {
     // TODO(brianwilkerson) Optimize this, by allowing support for source
     // factories to restore URI's from a file path rather than a source.
     Source source = file.createSource();
     if (context == null) {
       return source;
     }
+    if (context.sourceFactory == null) {
+      return null;
+    }
     Uri uri = context.sourceFactory.restoreUri(source);
     return file.createSource(uri);
   }
 
   static bool _shouldFileBeAnalyzed(File file) {
     if (!(AnalysisEngine.isDartFileName(file.path) ||
         AnalysisEngine.isHtmlFileName(file.path))) {
       return false;
     }
     // Emacs creates dummy links to track the fact that a file is open for
@@ skipping 85 matching lines @@
     return excludes(resource.path);
   }
 
   /**
    * Returns `true` if [path] is the pubspec file of this context.
    */
   bool isPubspec(String path) {
     return path == pubspecPath;
   }
 }