Fix snapshots from Downloads being deleted by last_n.

chrome/browser/android/offline_pages/request_coordinator_factory.cc

 // 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.
 
 #include "chrome/browser/android/offline_pages/request_coordinator_factory.h"
 
 #include <memory>
 
 #include "base/memory/ptr_util.h"
 #include "base/memory/singleton.h"
@@ skipping 25 matching lines @@
           BrowserContextDependencyManager::GetInstance()) {}
 
 // static
 RequestCoordinatorFactory* RequestCoordinatorFactory::GetInstance() {
   return base::Singleton<RequestCoordinatorFactory>::get();
 }
 
 // static
 RequestCoordinator* RequestCoordinatorFactory::GetForBrowserContext(
     content::BrowserContext* context) {
+  if (GetInstance()->always_nullptr_)
+    return nullptr;
   return static_cast<RequestCoordinator*>(
       GetInstance()->GetServiceForBrowserContext(context, true));
 }
 
 KeyedService* RequestCoordinatorFactory::BuildServiceInstanceFor(
     content::BrowserContext* context) const {
   std::unique_ptr<OfflinerPolicy> policy(new OfflinerPolicy());
   std::unique_ptr<OfflinerFactory> prerenderer_offliner(
       new PrerenderingOfflinerFactory(context));
 
@@ skipping 19 matching lines @@
       std::move(scheduler), network_quality_estimator);
 
   DownloadNotifyingObserver::CreateAndStartObserving(
       request_coordinator,
       base::MakeUnique<android::OfflinePageNotificationBridge>());
 
   return request_coordinator;
 }
 
 }  // namespace offline_pages