[Prerender] first contentful paint histograms.

chrome/browser/prerender/prerender_tab_helper.h

Index: chrome/browser/prerender/prerender_tab_helper.h
diff --git a/chrome/browser/prerender/prerender_tab_helper.h b/chrome/browser/prerender/prerender_tab_helper.h
index 2ded6bf8011420011a4c3b499793aa8c00621490..76bf74fd90fd079dad30d78a2e068fd9ee49a68b 100644
--- a/chrome/browser/prerender/prerender_tab_helper.h
+++ b/chrome/browser/prerender/prerender_tab_helper.h
@@ -52,6 +52,14 @@ class PrerenderTabHelper
   // 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>;
@@ -97,6 +105,14 @@ class PrerenderTabHelper
   // 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_;