[Background Fetch] Cleanup/fix thread safety

content/browser/background_fetch/background_fetch_data_manager.h

 // Copyright 2017 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 CONTENT_BROWSER_BACKGROUND_FETCH_BACKGROUND_FETCH_DATA_MANAGER_H_
 #define CONTENT_BROWSER_BACKGROUND_FETCH_BACKGROUND_FETCH_DATA_MANAGER_H_
 
 #include <map>
 #include <memory>
 #include <string>
 #include <unordered_map>
 
 #include "base/callback_forward.h"
 #include "base/macros.h"
 #include "base/optional.h"
+#include "base/sequence_checker.h"
 #include "content/browser/background_fetch/background_fetch_registration_id.h"
 #include "content/common/content_export.h"
 #include "third_party/WebKit/public/platform/modules/background_fetch/background_fetch.mojom.h"
 #include "url/origin.h"
 
 namespace content {
 
 class BackgroundFetchRequestInfo;
 struct BackgroundFetchSettledFetch;
 class BlobHandle;
@@ skipping 63 matching lines @@
 
   class RegistrationData;
 
   // The blob storage request with which response information will be stored.
   scoped_refptr<ChromeBlobStorageContext> blob_storage_context_;
 
   // Map of known background fetch registration ids to their associated data.
   std::map<BackgroundFetchRegistrationId, std::unique_ptr<RegistrationData>>
       registrations_;
 
+  SEQUENCE_CHECKER(sequence_checker_);
+
   base::WeakPtrFactory<BackgroundFetchDataManager> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(BackgroundFetchDataManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_BACKGROUND_FETCH_BACKGROUND_FETCH_DATA_MANAGER_H_