[Offline Pages] Set up the initial prefetching service.

components/offline_pages/core/prefetch/prefetch_service.h

Index: components/offline_pages/core/prefetch/prefetch_service.h
diff --git a/components/offline_pages/core/prefetch/prefetch_service.h b/components/offline_pages/core/prefetch/prefetch_service.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_CORE_PREFETCH_PREFETCH_SERVICE_H_
+#define COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_SERVICE_H_
+
+#include "components/keyed_service/core/keyed_service.h"
+#include "components/offline_pages/core/offline_page_item.h"
+
+class GURL;
+
+namespace offline_pages {
+
+// Main class for the Offline Pages Prefetching feature, which will ask a server
+// to package content from interesting URLs and send it to Chrome for
+// consumption while offline.
+class PrefetchService : public KeyedService {
+ public:
+  struct PrefetchURL {
+    // Used to differentiate URLs from different sources.  |name_space| should
+    // be unique per source. |id| can be anything useful to identify the page,
+    // but will not be used for deduplication.
+    ClientId client_id;
+
+    // This URL will be prefetched by the service.
+    GURL url;
+  };
+
+  ~PrefetchService() override = default;
+
+  // Called when a consumer has candidate URLs for the system to prefetch.
+  // Duplicates are accepted by the PrefetchService but ignored.
+  virtual void AddCandidatePrefetchURLs(
+      const std::vector<PrefetchURL>& prefetch_urls) = 0;
+
+  // Called when all existing suggestions are no longer considered valid for a
+  // given namespace.  The prefetch service should remove any URLs that
+  // have not yet started downloading within that namespace.
+  virtual void RemoveAllUnprocessedPrefetchURLs(
+      const std::string& name_space) = 0;
+
+  // Called to invalidate a single PrefetchURL entry identified by |client_id|.
+  // If multiple have the same |client_id|, they will all be removed.
+  virtual void RemovePrefetchURLsByClientId(const ClientId& client_id) = 0;
+};
+
+}  // namespace offline_pages
+
+#endif  // COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_SERVICE_IMPL_H_