Create skeleton for the Prefetching store and initial pipeline step.

components/offline_pages/content/suggested_articles_observer.cc

Index: components/offline_pages/content/suggested_articles_observer.cc
diff --git a/components/offline_pages/content/suggested_articles_observer.cc b/components/offline_pages/content/suggested_articles_observer.cc
index 4b60a286f7b9ab6682cf2637dce3c0b72bbb9dfe..a349ae4ed6ce63acc7686a5e1537cf7bf721de4a 100644
--- a/components/offline_pages/content/suggested_articles_observer.cc
+++ b/components/offline_pages/content/suggested_articles_observer.cc
@@ -14,6 +14,7 @@
 #include "components/offline_pages/core/offline_page_feature.h"
 #include "components/offline_pages/core/prefetch/prefetch_dispatcher.h"
 #include "components/offline_pages/core/prefetch/prefetch_service.h"
+#include "components/offline_pages/core/prefetch/prefetch_types.h"
 
 using ntp_snippets::Category;
 using ntp_snippets::ContentSuggestion;
@@ -30,10 +31,6 @@ const ntp_snippets::Category& ArticlesCategory() {
   return articles;
 }
 
-ClientId CreateClientIDFromSuggestionId(const ContentSuggestion::ID& id) {
-  return ClientId(kSuggestedArticlesNamespace, id.id_within_category());
-}
-
 // The default delegate that contains external dependencies for the Offline Page
 // Suggestions Observer.  This is unused in tests, which implement their own
 // Delegate.
@@ -101,10 +98,10 @@ void SuggestedArticlesObserver::OnNewSuggestions(Category category) {
   if (suggestions.empty())
     return;
 
-  std::vector<PrefetchDispatcher::PrefetchURL> prefetch_urls;
+  std::vector<PrefetchURL> prefetch_urls;
   for (const ContentSuggestion& suggestion : suggestions) {
     prefetch_urls.push_back(
-        {CreateClientIDFromSuggestionId(suggestion.id()), suggestion.url()});
+        {suggestion.id().id_within_category(), suggestion.url()});
   }
 
   PrefetchService* service = delegate_->GetPrefetchService(browser_context_);
@@ -113,7 +110,8 @@ void SuggestedArticlesObserver::OnNewSuggestions(Category category) {
                 "SuggestedArticlesObserver.";
     return;
   }
-  service->GetDispatcher()->AddCandidatePrefetchURLs(prefetch_urls);
+  service->GetDispatcher()->AddCandidatePrefetchURLs(
+      kSuggestedArticlesNamespace, prefetch_urls);
 }
 
 void SuggestedArticlesObserver::OnCategoryStatusChanged(
@@ -148,7 +146,7 @@ void SuggestedArticlesObserver::OnSuggestionInvalidated(
     return;
   }
   service->GetDispatcher()->RemovePrefetchURLsByClientId(
-      CreateClientIDFromSuggestionId(suggestion_id));
+      kSuggestedArticlesNamespace, suggestion_id.id_within_category());
 }
 
 void SuggestedArticlesObserver::OnFullRefreshRequired() {