[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 bc5db07e2888bac3e7f1423ef1c219a2d0db4591..5f96be28c3d8779e77883d3bb77545f9e770ed57 100644
--- a/chrome/browser/prerender/prerender_tab_helper.h
+++ b/chrome/browser/prerender/prerender_tab_helper.h
@@ -48,6 +48,10 @@ class PrerenderTabHelper
   // Called when this prerendered WebContents has just been swapped in.
   void PrerenderSwappedIn();
 
+  base::TimeTicks swap_ticks() const { return swap_ticks_; }
+
+  Origin origin() const { return origin_; }
+
  private:
   explicit PrerenderTabHelper(content::WebContents* web_contents);
   friend class content::WebContentsUserData<PrerenderTabHelper>;
@@ -86,6 +90,10 @@ 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 swap_ticks_;
+
   // Current URL being loaded.
   GURL url_;