Generalize Previews Type code

components/previews/core/previews_opt_out_store.h

Index: components/previews/core/previews_opt_out_store.h
diff --git a/components/previews/core/previews_opt_out_store.h b/components/previews/core/previews_opt_out_store.h
index 15aa73f3f9c104ddb354350f64471c207ed37687..5e078686c03328924b8feff41af47639bba29191 100644
--- a/components/previews/core/previews_opt_out_store.h
+++ b/components/previews/core/previews_opt_out_store.h
@@ -8,31 +8,26 @@
 #include <stdint.h>
 
 #include <memory>
 #include <string>
 #include <unordered_map>
 #include <vector>
 
 #include "base/callback.h"
 #include "base/time/time.h"
 #include "components/previews/core/previews_black_list_item.h"
+#include "components/previews/core/previews_experiments.h"
 
 class GURL;
 
 namespace previews {
 
-enum class PreviewsType {
-  NONE = 0,
-  OFFLINE = 1,
-  LAST = 2,
-};
-
 typedef std::unordered_map<std::string, std::unique_ptr<PreviewsBlackListItem>>
     BlackListItemMap;
 
 typedef base::Callback<void(std::unique_ptr<BlackListItemMap>)>
     LoadBlackListCallback;
 
 // PreviewsOptOutStore keeps opt out information for the previews.
 // Ability to create multiple instances of the store as well as behavior of
 // asynchronous operations when the object is being destroyed, before such
 // operation finishes will depend on implementation. It is possible to issue