Create skeleton for the Prefetching store and initial pipeline step.

components/offline_pages/core/prefetch/prefetch_types.h

Index: components/offline_pages/core/prefetch/prefetch_types.h
diff --git a/components/offline_pages/core/prefetch/prefetch_types.h b/components/offline_pages/core/prefetch/prefetch_types.h
index c15b6a0e014dfa0d9e6dc45b2514ed8180e8e8c7..c6c1a2224889debea1c75e2d9d84d85e042f897b 100644
--- a/components/offline_pages/core/prefetch/prefetch_types.h
+++ b/components/offline_pages/core/prefetch/prefetch_types.h
@@ -5,9 +5,12 @@
 #ifndef COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_TYPES_H_
 #define COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_TYPES_H_
 
-#include "base/macros.h"
+#include <string>
+
 #include "base/time/time.h"
 
+#include "url/gurl.h"
+
 namespace offline_pages {
 
 // Status for sending prefetch request to the server.
@@ -99,6 +102,20 @@ enum class PrefetchItemErrorCode {
   EXPIRED,
 };
 
+// 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;
+
+  // This URL will be prefetched by the service.
+  GURL url;
+};
+
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_TYPES_H_