[Prerender] first contentful paint histograms.

chrome/browser/prerender/prerender_tab_helper.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_TAB_HELPER_H_
 #define CHROME_BROWSER_PRERENDER_PRERENDER_TAB_HELPER_H_
 
 #include <memory>
 
 #include "base/macros.h"
@@ skipping 34 matching lines @@
   // Called when the URL of the main frame changed, either when the load
   // commits, or a redirect happens.
   void MainFrameUrlDidChange(const GURL& url);
 
   // Called when this prerendered WebContents has just been swapped in.
   void PrerenderSwappedIn();
 
   // Called when a control prerender is resolved. Applies to the next load.
   void WouldHavePrerenderedNextLoad(Origin origin);
 
+  // Computes the time delta from prerender load start to swapped in time. This
+  // adjustment is the difference between actual load or paint times and
+  // perceived times. Returns false if this is called outside the interval from
+  // swap in to page load.
+  bool LoadToPerceivedDelta(base::TimeDelta* delta);
+
+  Origin origin() const { return origin_; }
+
  private:
   explicit PrerenderTabHelper(content::WebContents* web_contents);
   friend class content::WebContentsUserData<PrerenderTabHelper>;
 
   void RecordPerceivedPageLoadTime(
       base::TimeDelta perceived_page_load_time,
       double fraction_plt_elapsed_at_swap_in);
 
   // Retrieves the PrerenderManager, or NULL, if none was found.
   PrerenderManager* MaybeGetPrerenderManager() const;
@@ skipping 25 matching lines @@
   // System time at which the current load was started for the purpose of
   // the perceived page load time (PPLT). If null, there is no current
   // load.
   base::TimeTicks pplt_load_start_;
 
   // System time at which the actual pageload started (pre-swapin), if
   // a applicable (in cases when a prerender that was still loading was
   // swapped in).
   base::TimeTicks actual_load_start_;
 
+  // Record the most recent load and swap times. These differ from
+  // |pplt_load_start_| and |actual_load_start_| in that they are not reset in
+  // various circumstances, like a load being stopped. There is no guarantee
+  // about their correctness. For example, if a load somehow starts after a
+  // swap, then |last_load_ > last_swap_|.
+  base::TimeTicks last_load_;
+  base::TimeTicks last_swap_;
+
   // Current URL being loaded.
   GURL url_;
 
   base::WeakPtrFactory<PrerenderTabHelper> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(PrerenderTabHelper);
 };
 
 }  // namespace prerender
 
 #endif  // CHROME_BROWSER_PRERENDER_PRERENDER_TAB_HELPER_H_