[NTP Snippets] Persist the set of snippets in a pref

components/ntp_snippets/ntp_snippets_service_unittest.cc

 // 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.
 
 #include "base/macros.h"
 #include "base/message_loop/message_loop.h"
 #include "base/thread_task_runner_handle.h"
 #include "base/time/time.h"
 #include "components/ntp_snippets/ntp_snippet.h"
 #include "components/ntp_snippets/ntp_snippets_fetcher.h"
@@ skipping 42 matching lines @@
   scoped_ptr<NTPSnippetsService> CreateSnippetService() {
     scoped_refptr<base::SingleThreadTaskRunner> task_runner(
         base::ThreadTaskRunnerHandle::Get());
     scoped_refptr<net::TestURLRequestContextGetter> request_context_getter =
         new net::TestURLRequestContextGetter(task_runner.get());
     FakeProfileOAuth2TokenService* token_service =
         new FakeProfileOAuth2TokenService();
     FakeSigninManagerBase* signin_manager =  new FakeSigninManagerBase(
         signin_client_.get(), account_tracker_.get());
 
-    scoped_ptr<NTPSnippetsService> service(
-        new NTPSnippetsService(task_runner.get(), std::string("fr"), nullptr,
-          make_scoped_ptr(new NTPSnippetsFetcher(task_runner.get(),
-            signin_manager, token_service, request_context_getter,
-            base::FilePath()))));
+    scoped_ptr<NTPSnippetsService> service(new NTPSnippetsService(
+        nullptr, task_runner.get(), std::string("fr"), nullptr,
+        make_scoped_ptr(new NTPSnippetsFetcher(
+            task_runner.get(), signin_manager, token_service,
+            request_context_getter, base::FilePath()))));
     return service;
   }
 
  private:
   scoped_ptr<AccountTrackerService> account_tracker_;
   scoped_ptr<TestSigninClient> signin_client_;
   base::MessageLoop message_loop_;
   DISALLOW_COPY_AND_ASSIGN(NTPSnippetsServiceTest);
 };
 
@@ skipping 86 matching lines @@
   EXPECT_TRUE(service->LoadFromJSONString(json_str));
 
   SnippetObserver observer;
   service->AddObserver(&observer);
 
   EXPECT_TRUE(observer.loaded_);
 
   service->RemoveObserver(&observer);
 }
 }  // namespace ntp_snippets