[Offline Pages] Add a GCMAppHandler for offline page prefetch.

components/offline_pages/core/prefetch/suggested_articles_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 COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_SUGGESTED_ARTICLES_OBSERVER_H_
+#define COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_SUGGESTED_ARTICLES_OBSERVER_H_
+
+#include <memory>
+
+#include "base/callback.h"
+#include "base/memory/weak_ptr.h"
+#include "components/ntp_snippets/content_suggestions_service.h"
+#include "components/offline_pages/core/prefetch/prefetch_service.h"
+
+namespace ntp_snippets {
+class Category;
+}
+
+namespace offline_pages {
+
+// Observes the ContentSuggestionsService, listening for new suggestions in the
+// ARTICLES category.  When those suggestions arrive, it then forwards them to
+// the Prefetch Service, which does not know about Content Suggestions
+// specifically.
+class SuggestedArticlesObserver
+    : public ntp_snippets::ContentSuggestionsService::Observer {
+ public:
+  SuggestedArticlesObserver(
+      // This can be |nullptr| in test.
+      ntp_snippets::ContentSuggestionsService* content_suggestions_service,
+      PrefetchService* prefetch_service);
+  ~SuggestedArticlesObserver() override;
+
+  // ContentSuggestionsService::Observer overrides.
+  void OnNewSuggestions(ntp_snippets::Category category) override;
+  void OnCategoryStatusChanged(
+      ntp_snippets::Category category,
+      ntp_snippets::CategoryStatus new_status) override;
+  void OnSuggestionInvalidated(
+      const ntp_snippets::ContentSuggestion::ID& suggestion_id) override;
+  void OnFullRefreshRequired() override;
+  void ContentSuggestionsServiceShutdown() override;
+
+  // Returns a pointer to the list of testing articles. If there is no such
+  // list, allocates one before returning the list.  The observer owns the list.
+  std::vector<ntp_snippets::ContentSuggestion>* GetTestingArticles();
+
+ private:
+  // Unowned, only used when we are called by observer methods (so the
+  // pointer will be valid).
+  ntp_snippets::ContentSuggestionsService* content_suggestions_service_;
+
+  // This class is owned by the prefetch service.
+  PrefetchService* prefetch_service_;
+
+  // Normally null, but can be set in tests to override the default behavior.
+  std::unique_ptr<std::vector<ntp_snippets::ContentSuggestion>> test_articles_;
+
+  ntp_snippets::CategoryStatus category_status_ =
+      ntp_snippets::CategoryStatus::INITIALIZING;
+
+  DISALLOW_COPY_AND_ASSIGN(SuggestedArticlesObserver);
+};
+
+}  // namespace offline_pages
+
+#endif  // COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_SUGGESTED_ARTICLES_OBSERVER_H_