[Offline Pages] Set up the initial prefetching service.

components/offline_pages/content/suggested_articles_observer.h

Index: components/offline_pages/content/suggested_articles_observer.h
diff --git a/components/offline_pages/content/suggested_articles_observer.h b/components/offline_pages/content/suggested_articles_observer.h
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+// 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,
+      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_