[Offline Pages] Set up the initial prefetching service.

components/offline_pages/core/prefetch/prefetch_service.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_PREFETCH_SERVICE_H_
+#define COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_SERVICE_H_
+
+#include "components/keyed_service/core/keyed_service.h"
+
+class GURL;
+
+namespace offline_pages {
+
+class PrefetchService : public KeyedService {

[carlosk, 2017/04/11 17:31:36]

Please add a comment explaining what this class represents.

[dewittj, 2017/04/11 21:25:49]

Done.

+ public:
+  ~PrefetchService() override = default;
+
+  // This will be called by OfflinePageSuggestionsObserver when suggestions

[carlosk, 2017/04/11 17:31:36]

nit: the potential caller should not be mentioned here.

[dewittj, 2017/04/11 21:25:48]

Done.

+  // that are not already saved into the OfflinePageModel are provided.
+  virtual void OnNewURLSuggestions(std::vector<GURL> suggested_urls) = 0;

[Dmitry Titov, 2017/04/11 01:17:14]

Not a request, but for consideration: Lets say at some point we want to use this
similar to current RequestCoordinator, to ask to offline/download a page that
perhaps user requested. What if we split the "suggestions-related" functionality
into separate small class (maybe into the suggestions observer), so that
PrefetchService would simply expose something like DownloadPages(list-of-urls).

Eventually there will be a need for an Observer of some sort (either for
updating some in-progress UI, popping up re-engagement notification etc)

For this patch, if it is easy to avoid 'suggestions' to propagate into this
class, it'd be cool.

[dewittj, 2017/04/11 21:25:49]

Done.

+
+  // This will be called when all existing suggestions are no longer considered
+  // valid.  The prefetch service should remove any suggestions that have not
+  // yet started downloading.
+  virtual void RemoveAllUnprocessedURLSuggestions() = 0;
+};
+
+}  // namespace offline_pages
+
+#endif  // COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_SERVICE_IMPL_H_