(TBR) fix PubPackageMapProvider to use resourceProvider context for path

pkg/analyzer/lib/source/pub_package_map_provider.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 source.pub_package_map_provider;
 
 import 'dart:collection';
 import 'dart:convert';
 import 'dart:io' as io;
 
@@ skipping 78 matching lines @@
   }
 
   /**
    * Create a PackageMapInfo object representing an error condition.
    */
   PackageMapInfo computePackageMapError(Folder folder) {
     // Even if an error occurs, we still need to know the dependencies, so that
     // we'll know when to try running "pub list-package-dirs" again.
     // Unfortunately, "pub list-package-dirs" doesn't tell us dependencies when
     // an error occurs, so just assume there is one dependency, "pubspec.lock".
-    List<String> dependencies = <String>[join(folder.path, PUBSPEC_LOCK_NAME)];
+    List<String> dependencies = <String>[
+        resourceProvider.pathContext.join(folder.path, PUBSPEC_LOCK_NAME)];
     return new PackageMapInfo(null, dependencies.toSet());
   }
 
   /**
    * Decode the JSON output from pub into a package map.  Paths in the
    * output are considered relative to [folder].
    */
   PackageMapInfo parsePackageMap(Map obj, Folder folder) {
     // The output of pub looks like this:
     // {
@@ skipping 44 matching lines @@
   /**
    * Run pub list to determine the packages and input files.
    */
   io.ProcessResult _runPubListDefault(Folder folder) {
     return io.Process.runSync(
         sdk.pubExecutable.getAbsolutePath(),
         [PUB_LIST_COMMAND],
         workingDirectory: folder.path);
   }
 }