[NoStatePrefetch] Add performance 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 682968aeb11883507ebc21aaf7813ed1d51acadb..4acef7481f918029698a998ff068da066b32eb33 100644
--- a/chrome/browser/prerender/prerender_manager.cc
+++ b/chrome/browser/prerender/prerender_manager.cc
@@ -145,13 +145,12 @@ PrerenderManager::PrerenderManagerMode PrerenderManager::mode_ =
     PRERENDER_MODE_ENABLED;
 
 struct PrerenderManager::NavigationRecord {
-  NavigationRecord(const GURL& url, base::TimeTicks time)
-      : url(url),
-        time(time) {
-  }
+  NavigationRecord(const GURL& url, base::TimeTicks time, Origin origin)
+      : url(url), time(time), origin(origin) {}
 
   GURL url;
   base::TimeTicks time;
+  Origin origin;
 };
 
 PrerenderManager::PrerenderManager(Profile* profile)
@@ -566,6 +565,33 @@ void PrerenderManager::RecordPrefetchRedirectCount(Origin origin,
                                            redirect_count);
 }
 
+void PrerenderManager::RecordFirstContentfulPaint(const GURL& url,
+                                                  bool is_no_store,
+                                                  base::TimeDelta time) {

[mmenke, 2016/09/15 17:20:44]

Would it make more sense to pass along the WebContents instead?  Relying one
prerender of a URL seems like a bad idea.  Also worth noting that offline
prerenders may be able to violate that, so you end up with the wrong prerender.

[droger, 2016/09/16 12:21:50]

Sorry, I don't understand the concern.

Note that I don't need any WebContents here.

What this function does, is look if that URL was prefetched recently (note that
prefetch is different from prerender, in particular it does not matter if the
WebContents that was used for prefetch is still alive), and if so records how
long ago.

+  CleanUpOldNavigations(&prefetches_, base::TimeDelta::FromMinutes(30));
+
+  // Compute the prefetch age.
+  base::TimeDelta prefetch_age;
+  Origin origin = ORIGIN_NONE;
+  for (auto it = prefetches_.crbegin(); it != prefetches_.crend(); ++it) {
+    if (it->url == url) {
+      prefetch_age = GetCurrentTimeTicks() - it->time;
+      origin = it->origin;
+      break;
+    }
+  }
+
+  histograms_->RecordFirstContentfulPaint(origin, is_no_store, time,
+                                          prefetch_age);
+
+  // Loading a prefetched URL resets the revalidation bypass. Remove the url
+  // from the prefetch list for more accurate metrics.
+  prefetches_.erase(
+      std::remove_if(prefetches_.begin(), prefetches_.end(),
+                     [url](const NavigationRecord& r) { return r.url == url; }),
+      prefetches_.end());
+}
+
 // static
 PrerenderManager::PrerenderManagerMode PrerenderManager::GetMode() {
   return mode_;
@@ -692,7 +718,8 @@ bool PrerenderManager::HasRecentlyBeenNavigatedTo(Origin origin,
                                                   const GURL& url) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
-  CleanUpOldNavigations();
+  CleanUpOldNavigations(&navigations_, base::TimeDelta::FromMilliseconds(
+                                           kNavigationRecordWindowMs));
   for (auto it = navigations_.rbegin(); it != navigations_.rend(); ++it) {
     if (it->url == url) {
       base::TimeDelta delta = GetCurrentTimeTicks() - it->time;
@@ -776,8 +803,9 @@ void PrerenderManager::RecordFinalStatus(Origin origin,
 void PrerenderManager::RecordNavigation(const GURL& url) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
-  navigations_.push_back(NavigationRecord(url, GetCurrentTimeTicks()));
-  CleanUpOldNavigations();
+  navigations_.emplace_back(url, GetCurrentTimeTicks(), ORIGIN_NONE);
+  CleanUpOldNavigations(&navigations_, base::TimeDelta::FromMilliseconds(
+                                           kNavigationRecordWindowMs));
 }
 
 struct PrerenderManager::PrerenderData::OrderByExpiryTime {
@@ -957,6 +985,9 @@ std::unique_ptr<PrerenderHandle> PrerenderManager::AddPrerender(
   histograms_->RecordPrerenderStarted(origin);
   DCHECK(!prerender_contents_ptr->prerendering_has_started());
 
+  if (prerender_contents_ptr->prerender_mode() == PREFETCH_ONLY)
+    prefetches_.emplace_back(url, GetCurrentTimeTicks(), origin);
+
   std::unique_ptr<PrerenderHandle> prerender_handle =
       base::WrapUnique(new PrerenderHandle(active_prerenders_.back().get()));
   SortActivePrerenders();
@@ -1128,18 +1159,19 @@ void PrerenderManager::DeleteOldWebContents() {
   old_web_contents_list_.clear();
 }
 
-void PrerenderManager::CleanUpOldNavigations() {
+void PrerenderManager::CleanUpOldNavigations(
+    std::vector<NavigationRecord>* navigations,
+    base::TimeDelta max_age) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
   // Cutoff. Navigations before this cutoff can be discarded.
-  base::TimeTicks cutoff = GetCurrentTimeTicks() -
-      base::TimeDelta::FromMilliseconds(kNavigationRecordWindowMs);
-  auto it = navigations_.begin();
-  for (; it != navigations_.end(); ++it) {
+  base::TimeTicks cutoff = GetCurrentTimeTicks() - max_age;
+  auto it = navigations->begin();
+  for (; it != navigations->end(); ++it) {
     if (it->time > cutoff)
       break;
   }
-  navigations_.erase(navigations_.begin(), it);
+  navigations->erase(navigations->begin(), it);
 }
 
 void PrerenderManager::ScheduleDeleteOldWebContents(