[Background Fetch] Cleanup/fix thread safety

content/browser/background_fetch/background_fetch_service_impl.cc

 // 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.
 
 #include "content/browser/background_fetch/background_fetch_service_impl.h"
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
 #include "base/optional.h"
 #include "content/browser/background_fetch/background_fetch_context.h"
@@ skipping 33 matching lines @@
 }
 
 BackgroundFetchServiceImpl::BackgroundFetchServiceImpl(
     int render_process_id,
     scoped_refptr<BackgroundFetchContext> background_fetch_context)
     : render_process_id_(render_process_id),
       background_fetch_context_(std::move(background_fetch_context)) {
   DCHECK(background_fetch_context_);
 }
 
-BackgroundFetchServiceImpl::~BackgroundFetchServiceImpl() = default;
+BackgroundFetchServiceImpl::~BackgroundFetchServiceImpl() {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+}
 
 void BackgroundFetchServiceImpl::Fetch(
     int64_t service_worker_registration_id,
     const url::Origin& origin,
     const std::string& tag,
     const std::vector<ServiceWorkerFetchRequest>& requests,
     const BackgroundFetchOptions& options,
     FetchCallback callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   if (!ValidateTag(tag)) {
@@ skipping 135 matching lines @@
   if (title.empty() || title.size() > kMaxTitleLength) {
     bad_message::ReceivedBadMessage(render_process_id_,
                                     bad_message::BFSI_INVALID_TITLE);
     return false;
   }
 
   return true;
 }
 
 }  // namespace content