Always delete media galleries FilePathWatchers on the FILE thread.

chrome/browser/media_galleries/fileapi/file_path_watcher_util.cc

Index: chrome/browser/media_galleries/fileapi/file_path_watcher_util.cc
diff --git a/chrome/browser/media_galleries/fileapi/file_path_watcher_util.cc b/chrome/browser/media_galleries/fileapi/file_path_watcher_util.cc
index 16295c999a16981a1e4be8aea330e3473538a13e..05ca7426591375dbc7a4219d45cfdeb0da47e96c 100644
--- a/chrome/browser/media_galleries/fileapi/file_path_watcher_util.cc
+++ b/chrome/browser/media_galleries/fileapi/file_path_watcher_util.cc
@@ -33,7 +33,7 @@ void StartFilePathWatchOnFileThread(
   DCHECK_CURRENTLY_ON(content::BrowserThread::FILE);
   // The watcher is created on the FILE thread because it is very difficult
   // to safely pass an already-created file watcher to a different thread.
-  std::unique_ptr<base::FilePathWatcher> watcher(new base::FilePathWatcher);
+  MediaFilePathWatcherUniquePtr watcher(new base::FilePathWatcher);
   bool success = watcher->Watch(
       path,
       false /* recursive */,
@@ -58,15 +58,3 @@ void StartFilePathWatchOnMediaTaskRunner(
                                               watch_started_callback,
                                               path_changed_callback));
 }
-
-void StopFilePathWatchOnMediaTaskRunner(
-    std::unique_ptr<base::FilePathWatcher> watcher) {
-  MediaFileSystemBackend::AssertCurrentlyOnMediaSequence();
-  if (watcher) {
-    const bool task_posted = content::BrowserThread::DeleteSoon(
-        content::BrowserThread::FILE, FROM_HERE, watcher.release());
-
-    // This will fail if the FILE thread has been stopped.
-    DCHECK(task_posted);
-  }
-}