Local NTP: Introduce OneGoogleBarService

chrome/browser/search/one_google_bar/one_google_bar_service_observer.h

Index: chrome/browser/search/one_google_bar/one_google_bar_service_observer.h
diff --git a/chrome/browser/search/one_google_bar/one_google_bar_service_observer.h b/chrome/browser/search/one_google_bar/one_google_bar_service_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..c3327ee5f404ea54bd5a210c44a5d26135e92963
--- /dev/null
+++ b/chrome/browser/search/one_google_bar/one_google_bar_service_observer.h
@@ -0,0 +1,20 @@
+// 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_
+
+#include "base/optional.h"
+
+struct OneGoogleBarData;
+
+// Observer for OneGoogleBarService. Gets notified when the OneGoogleBarData
+// changes.
+class OneGoogleBarServiceObserver {
+ public:
+  virtual void OnOneGoogleBarDataChanged(
+      const base::Optional<OneGoogleBarData>& data) = 0;

[sfiera, 2017/04/13 15:18:31]

Since the service provides an accessor, I would be inclined to provide either
the service or nothing to the observer here, so that it's clear that there is
one correct way to get the value.

[Marc Treib, 2017/04/13 15:44:02]

Hm. I do like the idea of "one way to get the value", but it's also somewhat
less convenient for clients...

[sfiera, 2017/04/13 15:58:33]

Passing nothing would be a lot less convenient, since you'd have to save a
pointer to the service. Passing the service seems OK to me; use
service->one_google_bar_data() instead of data.

[Marc Treib, 2017/04/13 16:45:15]

Eeh, in my experience most observers need to keep a pointer to the service
around anyway. Here in particular, the one pending implementation does that.
I've removed the data param.

+};
+
+#endif  // CHROME_BROWSER_SEARCH_ONE_GOOGLE_BAR_ONE_GOOGLE_BAR_SERVICE_OBSERVER_H_