Always delete media galleries FilePathWatchers on the FILE thread.

chrome/browser/media_galleries/fileapi/picasa_data_provider_browsertest.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/media_galleries/fileapi/picasa_data_provider.h"
 
 #include <memory>
 #include <utility>
 #include <vector>
 
@@ skipping 139 matching lines @@
   }
 
   void SetAlbumMapsForTesting(const AlbumMap& album_map,
                               const AlbumMap& folder_map) {
     album_map_ = album_map;
     folder_map_ = folder_map;
   }
 
  private:
   void OnTempDirWatchStarted(
-      std::unique_ptr<base::FilePathWatcher> temp_dir_watcher) override {
+      MediaFilePathWatcherUniquePtr temp_dir_watcher) override {
     PicasaDataProvider::OnTempDirWatchStarted(std::move(temp_dir_watcher));
 
     file_watch_request_returned_ = true;
     for (std::vector<ReadyCallback>::const_iterator it =
              file_watch_started_callbacks_.begin();
          it != file_watch_started_callbacks_.end();
          ++it) {
       it->Run(temp_dir_watcher_.get() != NULL);
     }
     file_watch_started_callbacks_.clear();
@@ skipping 387 matching lines @@
                    base::Unretained(this)));
   }
 };
 
 IN_PROC_BROWSER_TEST_F(PicasaDataProviderInvalidateInflightAlbumsIndexerTest,
                        InvalidateInflightAlbumsIndexerTest) {
   RunTest();
 }
 
 }  // namespace picasa