[Offline Pages] Fix flaky test due to actual loading of database.

chrome/browser/android/offline_pages/offline_page_model_factory.h

 // Copyright 2015 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_OFFLINE_PAGE_MODEL_FACTORY_H_
 #define CHROME_BROWSER_ANDROID_OFFLINE_PAGES_OFFLINE_PAGE_MODEL_FACTORY_H_
 
 #include "base/macros.h"
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 
 namespace base {
 template <typename T>
 struct DefaultSingletonTraits;
 }  // namespace base
 
 namespace offline_pages {
 
 class OfflinePageModel;
 
 // A factory to create one unique OfflinePageModel. Offline pages are not
 // supported in incognito, and this class uses default implementation of
 // |GetBrowserContextToUse|.
 // TODO(fgorski): Add an integration test that ensures incognito users don't
 // save or open offline pages.
 class OfflinePageModelFactory : public BrowserContextKeyedServiceFactory {
  public:
   static OfflinePageModelFactory* GetInstance();
   static OfflinePageModel* GetForBrowserContext(
       content::BrowserContext* context);
+  static TestingFactoryFunction GetMockFactory();
 
  private:
   friend struct base::DefaultSingletonTraits<OfflinePageModelFactory>;
 
   OfflinePageModelFactory();
   ~OfflinePageModelFactory() override {}
 
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* context) const override;
 
   DISALLOW_COPY_AND_ASSIGN(OfflinePageModelFactory);
 };
 
 }  // namespace offline_pages
 
 #endif  // CHROME_BROWSER_ANDROID_OFFLINE_PAGES_OFFLINE_PAGE_MODEL_FACTORY_H_