Hook up LocalNtpSource to OneGoogleBarService

chrome/browser/search/one_google_bar/one_google_bar_service_observer.h

 // Copyright 2017 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_SEARCH_ONE_GOOGLE_BAR_ONE_GOOGLE_BAR_SERVICE_OBSERVER_H_
 #define CHROME_BROWSER_SEARCH_ONE_GOOGLE_BAR_ONE_GOOGLE_BAR_SERVICE_OBSERVER_H_
 
 // Observer for OneGoogleBarService.
 class OneGoogleBarServiceObserver {
  public:
-  // Called when the OneGoogleBarData changes. You can get the new data via
+  // Called when the OneGoogleBarData changes, including changes between null
+  // and non-null. You can get the new data via
   // OneGoogleBarService::one_google_bar_data().
   virtual void OnOneGoogleBarDataChanged() = 0;
+
+  // Called when an attempt to fetch the OneGoogleBarData failed. Note that if
+  // there was cached data before the failed fetch attempt, then
+  // OnOneGoogleBarDataChanged gets called first.
+  virtual void OnOneGoogleBarFetchFailed() {}
+
+  // Called when the OneGoogleBarService is shutting down. Observers that might
+  // outlive the service should use this to unregister themselves, and clear out
+  // any pointers to the service they might hold.
+  virtual void OnOneGoogleBarServiceShuttingDown() {}
 };
 
 #endif  // CHROME_BROWSER_SEARCH_ONE_GOOGLE_BAR_ONE_GOOGLE_BAR_SERVICE_OBSERVER_H_