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

components/offline_pages/content/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_CONTENT_SUGGESTED_ARTICLES_OBSERVER_H_
-#define COMPONENTS_OFFLINE_PAGES_CONTENT_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 content {
-class BrowserContext;
-}  // namespace content
-
-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 base::SupportsUserData::Data {
- public:
-  // Delegate exists to allow for dependency injection in unit tests.
-  // SuggestedArticlesObserver implements its own delegate, |DefaultDelegate| in
-  // the .cc file that forwards to the ContentSuggestionsService and the
-  // PrefetchServiceFactory.  Code inside |DefaultDelegate| should be as simple
-  // as possible, since it will only be covered by instrumentation/browser
-  // tests.
-  class Delegate {
-   public:
-    virtual const std::vector<ntp_snippets::ContentSuggestion>& GetSuggestions(
-        const ntp_snippets::Category& category) = 0;
-    virtual PrefetchService* GetPrefetchService(
-        content::BrowserContext* context) = 0;
-    virtual ~Delegate() = default;
-  };
-
-  // This API creates a new SuggestedArticlesObserver and adds it as an
-  // observer to the ContentSuggestionsService provided.  Its lifetime is
-  // managed by the ContentSuggestionsService.
-  static void ObserveContentSuggestionsService(
-      content::BrowserContext* browser_context,
-      ntp_snippets::ContentSuggestionsService* service);
-
-  SuggestedArticlesObserver(content::BrowserContext* browser_context,
-                            std::unique_ptr<Delegate> delegate);
-  ~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;
-
- private:
-  content::BrowserContext* browser_context_;
-  ntp_snippets::CategoryStatus category_status_ =
-      ntp_snippets::CategoryStatus::INITIALIZING;
-  std::unique_ptr<Delegate> delegate_;
-
-  DISALLOW_COPY_AND_ASSIGN(SuggestedArticlesObserver);
-};
-
-}  // namespace offline_pages
-
-#endif  // COMPONENTS_OFFLINE_PAGES_CONTENT_SUGGESTED_ARTICLES_OBSERVER_H_