Fix a crash in DownloadUIAddapter that happens when Java bridge is created/removed quickly while

components/offline_pages/downloads/download_ui_adapter.h

 // Copyright 2016 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.
 
 #ifndef COMPONENTS_OFFLINE_PAGE_DOWNLOADS_DOWNLOAD_UI_ADAPTER_H_
 #define COMPONENTS_OFFLINE_PAGE_DOWNLOADS_DOWNLOAD_UI_ADAPTER_H_
 
 #include <map>
 #include <memory>
 #include <string>
@@ skipping 99 matching lines @@
   // Always valid, this class is a member of the model.
   OfflinePageModel* model_;
 
   bool is_loaded_;
 
   // The cache of UI items. The key is DownloadUIItem.guid.
   DownloadUIItems items_;
 
   // The observers.
   base::ObserverList<Observer> observers_;
+  int observers_count_;
 
   base::WeakPtrFactory<DownloadUIAdapter> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadUIAdapter);
 };
 
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGE_DOWNLOADS_DOWNLOAD_UI_ADAPTER_H_