Always call StorageMonitor::RemoveObserver in ~MediaFileSystemRegistry.

chrome/browser/media_galleries/gallery_watch_manager.cc

 // Copyright 2014 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/gallery_watch_manager.h"
 
 #include <stddef.h>
 
 #include <tuple>
 
 #include "base/bind.h"
+#include "base/logging.h"
 #include "base/macros.h"
 #include "base/stl_util.h"
 #include "base/time/time.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/media_galleries/gallery_watch_manager_observer.h"
 #include "chrome/browser/media_galleries/media_file_system_registry.h"
 #include "chrome/browser/media_galleries/media_galleries_preferences_factory.h"
 #include "chrome/browser/profiles/profile.h"
 #include "components/keyed_service/content/browser_context_keyed_service_shutdown_notifier_factory.h"
 #include "components/storage_monitor/storage_monitor.h"
@@ skipping 154 matching lines @@
 GalleryWatchManager::GalleryWatchManager()
     : storage_monitor_observed_(false), weak_factory_(this) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   watch_manager_.reset(new FileWatchManager(base::Bind(
       &GalleryWatchManager::OnFilePathChanged, weak_factory_.GetWeakPtr())));
 }
 
 GalleryWatchManager::~GalleryWatchManager() {
   weak_factory_.InvalidateWeakPtrs();
 
-  if (storage_monitor_observed_ &&
-      storage_monitor::StorageMonitor::GetInstance()) {
+  if (storage_monitor_observed_) {
+    DCHECK(storage_monitor::StorageMonitor::GetInstance());
     storage_monitor::StorageMonitor::GetInstance()->RemoveObserver(this);
   }
 
   BrowserThread::DeleteSoon(
       BrowserThread::FILE, FROM_HERE, watch_manager_.release());
 }
 
 void GalleryWatchManager::AddObserver(BrowserContext* browser_context,
                                       GalleryWatchManagerObserver* observer) {
   DCHECK(browser_context);
@@ skipping 295 matching lines @@
       DeactivateFileWatch(owner, it->second);
       // Post increment moves iterator to next element while deleting current.
       watches_.erase(it++);
       observers_[preferences->profile()]->OnGalleryWatchDropped(
           owner.extension_id, owner.gallery_id);
     } else {
       ++it;
     }
   }
 }