Fix snapshots from Downloads being deleted by last_n.

chrome/browser/android/offline_pages/request_coordinator_factory.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 CHROME_BROWSER_ANDROID_OFFLINE_PAGES_REQUEST_COORDINATOR_FACTORY_H_
 #define CHROME_BROWSER_ANDROID_OFFLINE_PAGES_REQUEST_COORDINATOR_FACTORY_H_
 
 #include "base/macros.h"
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 #include "content/public/browser/browser_context.h"
 
 namespace base {
 template <typename T>
 struct DefaultSingletonTraits;
 }  // namespace base
 
 namespace offline_pages {
 
 class RequestCoordinator;
 
 // A factory to create one unique RequestCoordinator.
 class RequestCoordinatorFactory : public BrowserContextKeyedServiceFactory {
  public:
   static RequestCoordinatorFactory* GetInstance();
   static RequestCoordinator* GetForBrowserContext(
       content::BrowserContext* context);
 
  private:
   friend struct base::DefaultSingletonTraits<RequestCoordinatorFactory>;
+  friend class RecentTabHelperTest;
 
   RequestCoordinatorFactory();
   ~RequestCoordinatorFactory() override {}
 
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* context) const override;
 
+  // Used to always return nullptr instances while running tests.
+  void ReturnNullptrForTesting(bool enabled) { always_nullptr_ = enabled; }

[fgorski, 2016/12/13 17:17:38]

I don't think changing anything about request coordinator should be necessary
here.

Did you try using: SetTestingFactoryAndUse
And passing in a method that returns nullptr?

As an alternative you can use this:
https://cs.chromium.org/chromium/src/chrome/browser/android/offline_pages/tes...
in your test. This method was build for what you are trying to do.
Example usage is in offline_page_utils_unittest.cc
https://cs.chromium.org/chromium/src/chrome/browser/android/offline_pages/off...

[carlosk, 2016/12/13 20:04:20]

Done. Thanks for pointing it out. I did not know about SetTestingFactoryAndUse.

+
+  bool always_nullptr_ = false;
+
   DISALLOW_COPY_AND_ASSIGN(RequestCoordinatorFactory);
 };
 
 }  // namespace offline_pages
 
 #endif  // CHROME_BROWSER_ANDROID_OFFLINE_PAGES_REQUEST_COORDINATOR_FACTORY_H_