Don't add files inside "packages" subdir to context.

pkg/analysis_server/lib/src/resource.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 resource;
 
 import 'dart:async';
 import 'dart:io' as io;
 
 import 'package:analyzer/src/generated/engine.dart' show TimestampedData;
@@ skipping 62 matching lines @@
 
 /**
  * Instances of the class [ResourceProvider] convert [String] paths into
  * [Resource]s.
  */
 abstract class ResourceProvider {
   /**
    * Return the [Resource] that corresponds to the given [path].
    */
   Resource getResource(String path);
+
+  /**
+   * Get the path context used by this resource provider.
+   */
+  Context get pathContext;
 }
 
 
 /**
  * An in-memory implementation of [Resource].
  */
 abstract class _MemoryResource implements Resource {
   final MemoryResourceProvider _provider;
   final String path;
 
@@ skipping 247 matching lines @@
     }
   }
 
   void deleteFile(String path) {
     _checkFileAtPath(path);
     _pathToResource.remove(path);
     _pathToContent.remove(path);
     _pathToTimestamp.remove(path);
     _notifyWatchers(path, ChangeType.REMOVE);
   }
+
+  @override
+  Context get pathContext => posix;
 }
 
 
 /**
  * A `dart:io` based implementation of [File].
  */
 class _PhysicalFile extends _PhysicalResource implements File {
   _PhysicalFile(io.File file) : super(file);
 
   @override
@@ skipping 75 matching lines @@
   @override
   Resource getResource(String path) {
     if (io.FileSystemEntity.isDirectorySync(path)) {
       io.Directory directory = new io.Directory(path);
       return new _PhysicalFolder(directory);
     } else {
       io.File file = new io.File(path);
       return new _PhysicalFile(file);
     }
   }
+
+  @override
+  Context get pathContext => io.Platform.isWindows ? windows : posix;
 }