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 f36526dcc7f3463bc56ad40c21c23eabe7755251..596c9a71d6ff60a9a391562ebfb498c896d55356 100644
--- a/components/offline_pages/core/prefetch/prefetch_types.h
+++ b/components/offline_pages/core/prefetch/prefetch_types.h
@@ -5,9 +5,11 @@
 #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 {
 
@@ -105,6 +107,20 @@ 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_