Require FilePathWatcher destructor to be called in sequence with Watch().

chrome/browser/media_galleries/fileapi/iapps_data_provider.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/iapps_data_provider.h"
 
 #include <map>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 22 matching lines @@
   DCHECK(!library_path_.empty());
 
   StartFilePathWatchOnMediaTaskRunner(
       library_path_,
       base::Bind(&IAppsDataProvider::OnLibraryWatchStarted,
                  weak_factory_.GetWeakPtr()),
       base::Bind(&IAppsDataProvider::OnLibraryChanged,
                  weak_factory_.GetWeakPtr()));
 }
 
-IAppsDataProvider::~IAppsDataProvider() {}
+IAppsDataProvider::~IAppsDataProvider() {
+  StopFilePathWatchOnMediaTaskRunner(std::move(library_watcher_));
+}
 
 bool IAppsDataProvider::valid() const {
   return is_valid_;
 }
 
 void IAppsDataProvider::set_valid(bool valid) {
   is_valid_ = valid;
 }
 
 void IAppsDataProvider::RefreshData(const ReadyCallback& ready_callback) {
@@ skipping 21 matching lines @@
 void IAppsDataProvider::OnLibraryChanged(const base::FilePath& path,
                                          bool error) {
   MediaFileSystemBackend::AssertCurrentlyOnMediaSequence();
   DCHECK_EQ(library_path_.value(), path.value());
   if (error)
     LOG(ERROR) << "Error watching " << library_path_.value();
   needs_refresh_ = true;
 }
 
 }  // namespace iapps