Prerender: clarify prerender origin for purposes of FCP histograms.

chrome/browser/prerender/prerender_manager.cc

Index: chrome/browser/prerender/prerender_manager.cc
diff --git a/chrome/browser/prerender/prerender_manager.cc b/chrome/browser/prerender/prerender_manager.cc
index 4d9f1adcbf5b3add7ef4b07e474bba16551fddc4..afe65ef76e6510b2105c0dab4129daccee4676ad 100644
--- a/chrome/browser/prerender/prerender_manager.cc
+++ b/chrome/browser/prerender/prerender_manager.cc
@@ -600,21 +600,23 @@ void PrerenderManager::RecordPrerenderFirstContentfulPaint(
   DCHECK(tab_helper);
 
   base::TimeDelta prefetch_age;
-  // The origin at prefetch is superceeded by the tab_helper origin for the
-  // histogram recording, below.
-  GetPrefetchInformation(url, &prefetch_age, nullptr);
+  Origin origin;
+  // The tab_helper origin is arguably more accurate, but in order to be
+  // consistent with other prefetch TTFCP histograms, the origin from
+  // GetPrefetchInformation is used instead.
+  GetPrefetchInformation(url, &prefetch_age, &origin);
   OnPrefetchUsed(url);
 
   base::TimeTicks swap_ticks = tab_helper->swap_ticks();
   bool fcp_recorded = false;
   if (!swap_ticks.is_null() && !first_contentful_paint.is_null()) {

[pasko, 2017/03/24 16:10:30]

this is only recorded when swap happened (!swap_ticks.is_null()), so it would
not be able to record "Reference", right?

then why changing an origin here matters for "Reference"?

[mattcary, 2017/03/27 07:52:05]

Or, it could perhaps be that my logic on the client-side redirect is wrong, and
in the prerender case we retain the original URL of the webcontents?

[pasko, 2017/03/27 17:32:57]

Sorry, I misread. We are recording "Reference" with Prerender in presence of a
client redirect (because the new PageLoadExtraInfo.start_url does not match
anything in prefetches_).

     histograms_->RecordPrefetchFirstContentfulPaintTime(
-        tab_helper->origin(), is_no_store, was_hidden,
-        first_contentful_paint - swap_ticks, prefetch_age);
+        origin, is_no_store, was_hidden, first_contentful_paint - swap_ticks,
+        prefetch_age);
     fcp_recorded = true;
   }
-  histograms_->RecordPerceivedFirstContentfulPaintStatus(
-      tab_helper->origin(), fcp_recorded, was_hidden);
+  histograms_->RecordPerceivedFirstContentfulPaintStatus(origin, fcp_recorded,
+                                                         was_hidden);
 
   for (auto& observer : observers_) {
     observer->OnFirstContentfulPaint();