[NoStatePrefetch] Add performance histograms.

chrome/browser/prerender/prerender_histograms.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_PRERENDER_PRERENDER_HISTOGRAMS_H_
 #define CHROME_BROWSER_PRERENDER_PRERENDER_HISTOGRAMS_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 103 matching lines @@
                                       bool is_main_resource,
                                       bool is_redirect,
                                       bool is_no_store) const;
 
   // Called when a NoStatePrefetch resource has been loaded. This is called only
   // once per resource, when all redirects have been resolved.
   void RecordPrefetchRedirectCount(Origin origin,
                                    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;
 
   // Returns the time elapsed since the last prerender happened.
   base::TimeDelta GetTimeSinceLastPrerender() const;
 
   // Returns whether the PrerenderManager is currently within the prerender
   // window - effectively, up to 30 seconds after a prerender tag has been
   // observed.
   bool WithinWindow() const;
@@ skipping 20 matching lines @@
   bool seen_pageload_started_after_prerender_;
 
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(PrerenderHistograms);
 };
 
 }  // namespace prerender
 
 #endif  // CHROME_BROWSER_PRERENDER_PRERENDER_HISTOGRAMS_H_