[Offline Pages] Set up the initial prefetching service.

chrome/browser/android/offline_pages/suggestions_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_ANDROID_OFFLINE_PAGES_SUGGESTIONS_OBSERVER_H_
+#define CHROME_BROWSER_ANDROID_OFFLINE_PAGES_SUGGESTIONS_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 of a
+// single category (initially ARTICLES).  When those suggestions arrive, it

[jianli, 2017/04/18 00:41:00]

Do we have a plan to make SuggestionsObserver support other category in the
future? If not, this class should be strictly associated with articles, like
renaming to SuggestedArticlesObserver. Otherwise, we should make it more
flexible by passing the hard-coded values from outside.

[dewittj, 2017/04/18 18:20:25]

Done.

+// then forwards them to the Prefetch Service, which does not know about Content
+// Suggestions specifically.
+class SuggestionsObserver
+    : public ntp_snippets::ContentSuggestionsService::Observer,
+      base::SupportsUserData::Data {
+ public:
+  // Delegate exists to allow for dependency injection in unit tests.
+  // SuggestionsObserver 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 SuggestionsObserver 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);
+
+  SuggestionsObserver(content::BrowserContext* browser_context,
+                      const ntp_snippets::Category& category,
+                      std::unique_ptr<Delegate> delegate);
+  ~SuggestionsObserver() 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;
+  ntp_snippets::Category category_;
+  std::unique_ptr<Delegate> delegate_;
+
+  DISALLOW_COPY_AND_ASSIGN(SuggestionsObserver);
+};
+
+}  // namespace offline_pages
+
+#endif  // CHROME_BROWSER_ANDROID_OFFLINE_PAGES_SUGGESTIONS_OBSERVER_H_