[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..9210f1618ca5859f58a9955c79cdfcba89f9ca96 100644
--- a/chrome/browser/prerender/prerender_tab_helper.h
+++ b/chrome/browser/prerender/prerender_tab_helper.h
@@ -52,6 +52,10 @@ class PrerenderTabHelper
   // Called when a control prerender is resolved. Applies to the next load.
   void WouldHavePrerenderedNextLoad(Origin origin);
 
+  base::TimeTicks last_swap() const { return last_swap_; }
+
+  Origin origin() const { return origin_; }
+
  private:
   explicit PrerenderTabHelper(content::WebContents* web_contents);
   friend class content::WebContentsUserData<PrerenderTabHelper>;
@@ -97,6 +101,10 @@ class PrerenderTabHelper
   // swapped in).
   base::TimeTicks actual_load_start_;
 
+  // Record the most recent swap time. This differs from |pplt_load_start_| in
+  // that it is not reset in various circumstances, like a load being stopped.
+  base::TimeTicks last_swap_;
+
   // Current URL being loaded.
   GURL url_;