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

chrome/browser/media_galleries/fileapi/iapps_data_provider.cc

Index: chrome/browser/media_galleries/fileapi/iapps_data_provider.cc
diff --git a/chrome/browser/media_galleries/fileapi/iapps_data_provider.cc b/chrome/browser/media_galleries/fileapi/iapps_data_provider.cc
index ec8cfd26052ca1382fdf018aeb8bf42a86ed1656..72e90365ceeac4d58d07b4bdafd9f8e8c50685ba 100644
--- a/chrome/browser/media_galleries/fileapi/iapps_data_provider.cc
+++ b/chrome/browser/media_galleries/fileapi/iapps_data_provider.cc
@@ -40,7 +40,9 @@ IAppsDataProvider::IAppsDataProvider(const base::FilePath& library_path)
                  weak_factory_.GetWeakPtr()));
 }
 
-IAppsDataProvider::~IAppsDataProvider() {}
+IAppsDataProvider::~IAppsDataProvider() {
+  StopFilePathWatchOnMediaTaskRunner(std::move(library_watcher_));
+}
 
 bool IAppsDataProvider::valid() const {
   return is_valid_;