[NoStatePrefetch] Add UMA histogram to count prefetch requests

chrome/browser/prerender/prerender_manager.h

Index: chrome/browser/prerender/prerender_manager.h
diff --git a/chrome/browser/prerender/prerender_manager.h b/chrome/browser/prerender/prerender_manager.h
index 0dbc1329c4c9f5f046f96975ccaf5908c8f890c8..47ad9e50e375a7ea7ac01645aa5589c34cf14ad9 100644
--- a/chrome/browser/prerender/prerender_manager.h
+++ b/chrome/browser/prerender/prerender_manager.h
@@ -199,6 +199,11 @@ class PrerenderManager : public base::SupportsWeakPtr<PrerenderManager>,
       double fraction_plt_elapsed_at_swap_in,
       const GURL& url);
 
+  // Called when a resource has been loaded by NoStatePrefetch.
+  void RecordResourcePrefetch(Origin origin,
+                              bool is_main_resource,
+                              bool is_no_store);
+
   static PrerenderManagerMode GetMode();
   static void SetMode(PrerenderManagerMode mode);
   static bool IsPrerenderingPossible();