Always delete media galleries FilePathWatchers on the FILE thread.

chrome/browser/media_galleries/fileapi/file_path_watcher_util.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/file_path_watcher_util.h"
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/location.h"
 #include "base/logging.h"
@@ skipping 15 matching lines @@
 
 // The watch has to be started on the FILE thread, and the callback called by
 // the FilePathWatcher also needs to run on the FILE thread.
 void StartFilePathWatchOnFileThread(
     const base::FilePath& path,
     const FileWatchStartedCallback& watch_started_callback,
     const base::FilePathWatcher::Callback& path_changed_callback) {
   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 */,
       base::Bind(&OnFilePathChangedOnFileThread, path_changed_callback));
   if (!success)
     LOG(ERROR) << "Adding watch for " << path.value() << " failed";
   MediaFileSystemBackend::MediaTaskRunner()->PostTask(
       FROM_HERE, base::Bind(watch_started_callback, base::Passed(&watcher)));
 }
 
 }  // namespace
 
 void StartFilePathWatchOnMediaTaskRunner(
     const base::FilePath& path,
     const FileWatchStartedCallback& watch_started_callback,
     const base::FilePathWatcher::Callback& path_changed_callback) {
   MediaFileSystemBackend::AssertCurrentlyOnMediaSequence();
   content::BrowserThread::PostTask(content::BrowserThread::FILE,
                                    FROM_HERE,
                                    base::Bind(&StartFilePathWatchOnFileThread,
                                               path,
                                               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);
-  }
-}