[NoStatePrefetch] Add performance histograms.

chrome/browser/prerender/prerender_histograms.h

Index: chrome/browser/prerender/prerender_histograms.h
diff --git a/chrome/browser/prerender/prerender_histograms.h b/chrome/browser/prerender/prerender_histograms.h
index 77f9f3549b81665cd30231bc71d9e8ad487edf3b..eeb44b9d0ef0bcae34ffa4d297d47a2e41abf33f 100644
--- a/chrome/browser/prerender/prerender_histograms.h
+++ b/chrome/browser/prerender/prerender_histograms.h
@@ -121,6 +121,15 @@ class PrerenderHistograms {
                                    bool is_main_resource,
                                    int redirect_count) const;
 
+  // Records the time to first contentful paint.
+  // |is_no_store| must be true if the main resource has a "no-store" cache
+  // control HTTP header.
+  // |prefetch_age| must be zero if the page was not prefetched.
+  void RecordFirstContentfulPaint(Origin origin,
+                                  bool is_no_store,
+                                  base::TimeDelta time,
+                                  base::TimeDelta prefetch_age);
+
  private:
   base::TimeTicks GetCurrentTimeTicks() const;