[NTP Snippets] Add a pref to disable the NTPSnippetsService

components/ntp_snippets/ntp_snippets_status_service.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_NTP_SNIPPETS_NTP_SNIPPETS_STATUS_SERVICE_H_
 #define COMPONENTS_NTP_SNIPPETS_NTP_SNIPPETS_STATUS_SERVICE_H_
 
 #include "base/callback.h"
 #include "base/gtest_prod_util.h"
 #include "base/scoped_observer.h"
+#include "components/prefs/pref_change_registrar.h"
 #include "components/sync_driver/sync_service_observer.h"
 
+class PrefRegistrySimple;
+class PrefService;
 class SigninManagerBase;
 
 namespace sync_driver {
 class SyncService;
 }
 
 namespace ntp_snippets {
 
 // On Android builds, a Java counterpart will be generated for this enum.
 // GENERATED_JAVA_ENUM_PACKAGE: org.chromium.chrome.browser.ntp.snippets
@@ skipping 14 matching lines @@
   HISTORY_SYNC_STATE_UNKNOWN
 };
 
 // Aggregates data from sync and signin to notify the snippet service of
 // relevant changes in their states.
 class NTPSnippetsStatusService : public sync_driver::SyncServiceObserver {
  public:
   typedef base::Callback<void(DisabledReason)> DisabledReasonChangeCallback;
 
   NTPSnippetsStatusService(SigninManagerBase* signin_manager,
-                           sync_driver::SyncService* sync_service);
+                           sync_driver::SyncService* sync_service,
+                           PrefService* pref_service);
 
   ~NTPSnippetsStatusService() override;
 
+  static void RegisterProfilePrefs(PrefRegistrySimple* registry);
+
   // Starts listening for changes from the dependencies. |callback| will be
   // called when a significant change in state is detected.
   void Init(const DisabledReasonChangeCallback& callback);
 
   DisabledReason disabled_reason() const { return disabled_reason_; }
 
  private:
   FRIEND_TEST_ALL_PREFIXES(NTPSnippetsStatusServiceTest,
                            SyncStateCompatibility);
+  FRIEND_TEST_ALL_PREFIXES(NTPSnippetsStatusServiceTest, DisabledViaPref);
 
-  // sync_driver::SyncServiceObserver implementation
+  // sync_driver::SyncServiceObserver implementation. Also used as a callback
+  // for the PrefChangeRegistrar.
   void OnStateChanged() override;
 
   DisabledReason GetDisabledReasonFromDeps() const;
 
   DisabledReason disabled_reason_;
   DisabledReasonChangeCallback disabled_reason_change_callback_;
 
   SigninManagerBase* signin_manager_;
   sync_driver::SyncService* sync_service_;
+  PrefService* pref_service_;
+
+  PrefChangeRegistrar pref_change_registrar_;
 
   // The observer for the SyncService. When the sync state changes,
   // SyncService will call |OnStateChanged|.
   ScopedObserver<sync_driver::SyncService, sync_driver::SyncServiceObserver>
       sync_service_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(NTPSnippetsStatusService);
 };
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_NTP_SNIPPETS_STATUS_SERVICE_H_