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

components/offline_pages/stub_offline_page_model.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 COMPONENTS_OFFLINE_PAGES_STUB_OFFLINE_PAGE_MODEL_H_
 #define COMPONENTS_OFFLINE_PAGES_STUB_OFFLINE_PAGE_MODEL_H_
 
 #include <set>
 #include <string>
 #include <vector>
 
+#include "components/keyed_service/core/keyed_service.h"
 #include "components/offline_pages/offline_page_model.h"
 
 namespace offline_pages {
 
 // Stub implementation of OfflinePageModel interface for testing. Besides using
 // as a stub for tests, it may also be subclassed to mock specific methods
 // needed for a set of tests.
-class StubOfflinePageModel : public OfflinePageModel {
+class StubOfflinePageModel : public OfflinePageModel, public KeyedService {
  public:
   StubOfflinePageModel();
   ~StubOfflinePageModel() override;
 
   void AddObserver(Observer* observer) override;
   void RemoveObserver(Observer* observer) override;
   void SavePage(const GURL& url,
                 const ClientId& client_id,
                 int64_t proposed_offline_id,
                 std::unique_ptr<OfflinePageArchiver> archiver,
@@ skipping 41 matching lines @@
   bool is_loaded() const override;
   OfflineEventLogger* GetLogger() override;
 
  private:
   std::vector<int64_t> offline_ids_;
 };
 
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_STUB_OFFLINE_PAGE_MODEL_H_