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 9e5ec6cbf624796bcf6e14499e9a367ded03c657..24a9f830525720ccdffe3f44cdc7f1bfed5578ce 100644
--- a/components/offline_pages/core/prefetch/prefetch_service.h
+++ b/components/offline_pages/core/prefetch/prefetch_service.h
@@ -8,8 +8,8 @@
 #include "components/keyed_service/core/keyed_service.h"
 
 namespace offline_pages {
-
 class PrefetchDispatcher;
+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.
@@ -18,6 +18,7 @@ class PrefetchService : public KeyedService {
   ~PrefetchService() override = default;
 
   virtual PrefetchDispatcher* GetDispatcher() = 0;

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

Why are these public?
How do you intend to use the service?

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

The service is supposed to be the ownership holder of all prefetching
sub-components, hence this getter. But I see where your doubt comes from and how
this could be influenced by the design of the store.

+  virtual PrefetchStore* GetStore() = 0;

[Dmitry Titov, 2017/05/26 23:05:06]

I think it would be more consistent to either have

virtual Store* GetStore();  // this likely needs a new namespace
or
virtual PrefetchStore* GetPrefetchStore()

same for GetDispatcher above...

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

Done.

 };
 
 }  // namespace offline_pages