Create skeleton for the Prefetching store and initial pipeline step.

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
index e8ceeccb3595533891dab2e6df81d3347cec09ee..d84bb9fcac3ddecff70a42f825571e95b4edb61d 100644
--- a/components/offline_pages/core/prefetch/prefetch_service.h
+++ b/components/offline_pages/core/prefetch/prefetch_service.h
@@ -12,10 +12,10 @@ class ContentSuggestionsService;
 }
 
 namespace offline_pages {
-
 class OfflineMetricsCollector;
 class PrefetchDispatcher;
 class PrefetchGCMHandler;
+class PrefetchStore;
 
 // Main class and entry point for the Offline Pages Prefetching feature, that
 // controls the lifetime of all major subcomponents of the prefetching system.
@@ -28,9 +28,10 @@ class PrefetchService : public KeyedService {
   // The service manages lifetime, hookup and initialization of Prefetch
   // system that consists of multiple specialized objects, all vended by this
   // service. All pointers are raw and are always valid.
-  virtual PrefetchDispatcher* GetDispatcher() = 0;
   virtual OfflineMetricsCollector* GetOfflineMetricsCollector() = 0;
+  virtual PrefetchDispatcher* GetPrefetchDispatcher() = 0;
   virtual PrefetchGCMHandler* GetPrefetchGCMHandler() = 0;
+  virtual PrefetchStore* GetPrefetchStore() = 0;
 
   // Called at construction of the ContentSuggestionsService to begin observing
   // events related to incoming articles.