Create skeleton for the Prefetching store and initial pipeline step.

components/offline_pages/core/prefetch/prefetch_types.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_TYPES_H_
 #define COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_TYPES_H_
 
+#include <string>
 #include <vector>
-#include "base/macros.h"
+
 #include "base/time/time.h"
+#include "url/gurl.h"
 
 namespace offline_pages {
 
 // Status for sending prefetch request to the server.
 enum class PrefetchRequestStatus {
   // Request completed successfully.
   SUCCESS,
   // Request failed due to to local network problem, unrelated to server load
   // levels. The caller will simply reschedule the retry in the next available
   // WiFi window after 15 minutes have passed.
@@ skipping 77 matching lines @@
 enum class PrefetchItemErrorCode {
   SUCCESS,
   EXPIRED,
 };
 
 // Callback invoked upon completion of a prefetch request.
 using PrefetchRequestFinishedCallback =
     base::Callback<void(PrefetchRequestStatus status,
                         const std::vector<RenderPageInfo>& pages)>;
 
+// Holds information about a new URL to be prefetched.
+struct PrefetchURL {
+  PrefetchURL(const std::string& client_id, const GURL& url)
+      : client_id(client_id), url(url) {}
+
+  // Client provided ID to allow the matching of URLs to the respective work
+  // item in the prefetching system. It can be anything useful to identify the
+  // page . It will not be used internally for de-duplication.
+  std::string client_id;

[fgorski, 2017/05/30 17:21:45]

You are overloading the term Client ID.
Is that intended? and what is the thinking behind it? 

[carlosk, 2017/06/01 01:49:59]

It would have the same objective as the existing ClientId, hence the very
similar naming which was indeed overloading that concept with only a part of it.

With the revert to using ClientId I expect this will not be a concern anymore.

+
+  // This URL will be prefetched by the service.
+  GURL url;
+};
+
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_TYPES_H_