Add a PLT histogram for prerender local predictor prefetches.

chrome/browser/prerender/prerender_local_predictor.cc

Index: chrome/browser/prerender/prerender_local_predictor.cc
diff --git a/chrome/browser/prerender/prerender_local_predictor.cc b/chrome/browser/prerender/prerender_local_predictor.cc
index fea2cafb090a314d5f4edad011f8e296b1e7815a..36ad713f48d45e132c1113620d86f386f73c1695 100644
--- a/chrome/browser/prerender/prerender_local_predictor.cc
+++ b/chrome/browser/prerender/prerender_local_predictor.cc
@@ -455,24 +455,55 @@ class PrerenderLocalPredictor::PrefetchList {
       return_value = true;
     }
     // If the item has been seen in both the history and in tab contents,
-    // erase it from the map to make room for new prefetches.
-    if (it->second->seen_tabcontents_ && it->second->seen_history_)
+    // and the page load time has been recorded, erase it from the map to
+    // make room for new prefetches.
+    if (it->second->seen_tabcontents_ && it->second->seen_history_ &&
+        it->second->plt_recorded_) {
       entries_.erase(url.spec().c_str());
+    }
     return return_value;
   }
 
+  // To be called when a PLT was seen for a given URL.
+  // Returns true iff:
+  // - There is an entry of a prefetch for the URL provided.
+  // - The prefetch was started before the page load was started (based on the
+  //   plt).
+  // - The prefetch entry has not been returned "true" for as a result of a call
+  //   to this method previously.
+  bool SeenPLTForURL(const GURL& url, base::TimeDelta plt) {

[jkarlin, 2014/08/21 14:34:14]

Rename to MarkPLTSeen?  Then reformat the comments to look more like MarkURLSeen
as well, as those are clearer.

// Marks the PLT for the provided URL as seen in the context specified.  Returns
true iff ... i.e. the marking was successful.

[tburkard, 2014/08/21 15:28:11]

Done.

+    ExpireOldItems();
+    base::hash_map<string, ListEntry*>::iterator it =
+        entries_.find(url.spec().c_str());
+    if (it == entries_.end() || it->second->plt_recorded_ ||
+        it->second->add_time_ > GetCurrentTime() - plt) {
+      return false;
+    }
+    it->second->plt_recorded_ = true;
+    // If the item has been seen in both the history and in tab contents,
+    // and the page load time has been recorded, erase it from the map to
+    // make room for new prefetches.
+    if (it->second->seen_tabcontents_ && it->second->seen_history_ &&
+        it->second->plt_recorded_) {
+      entries_.erase(url.spec().c_str());
+    }
+    return true;
+  }
+
  private:
   struct ListEntry {
     explicit ListEntry(const string& url)
         : url_(url),
           add_time_(GetCurrentTime()),
           seen_tabcontents_(false),
-          seen_history_(false) {
+          seen_history_(false),
+          plt_recorded_(false) {
     }
     std::string url_;
     base::Time add_time_;
     bool seen_tabcontents_;
     bool seen_history_;
+    bool plt_recorded_;

[jkarlin, 2014/08/21 14:34:14]

Why not seen_plt_ like the other members?  PrefetchList doesn't actually do the
recording.

[tburkard, 2014/08/21 15:28:11]

Done.

   };
 
   void ExpireOldItems() {
@@ -1119,6 +1150,14 @@ void PrerenderLocalPredictor::Init() {
 
 void PrerenderLocalPredictor::OnPLTEventForURL(const GURL& url,
                                                base::TimeDelta page_load_time) {
+  if (prefetch_list_->SeenPLTForURL(url, page_load_time)) {
+    UMA_HISTOGRAM_CUSTOM_TIMES("Prerender.LocalPredictorPrefetchMatchPLT",
+                               page_load_time,
+                               base::TimeDelta::FromMilliseconds(10),
+                               base::TimeDelta::FromSeconds(60),
+                               100);
+  }
+
   scoped_ptr<PrerenderProperties> prerender;
   if (DoesPrerenderMatchPLTRecord(last_swapped_in_prerender_.get(),
                                   url, page_load_time)) {
@@ -1338,8 +1377,19 @@ void PrerenderLocalPredictor::IssuePrerender(
     CandidatePrerenderInfo* info,
     LocalPredictorURLInfo* url_info) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  if (prefetch_list_->AddURL(url_info->url))
+  if (prefetch_list_->AddURL(url_info->url)) {
     RecordEvent(EVENT_PREFETCH_LIST_ADDED);
+    // If we are prefetching rather than prerendering, now is the time to launch
+    // the prefetch.
+    if (IsLocalPredictorPrerenderPrefetchEnabled()) {
+      // Obtain the render frame host that caused this prefetch.
+      RenderFrameHost* rfh = RenderFrameHost::FromID(info->render_process_id_,
+                                                     info->render_frame_id_);
+      // If it is still alive, launch the prefresh.
+      if (rfh)
+        rfh->Send(new PrefetchMsg_Prefetch(rfh->GetRoutingID(), url_info->url));
+    }
+  }
   PrerenderProperties* prerender_properties =
       GetIssuedPrerenderSlotForPriority(url_info->url, url_info->priority);
   if (!prerender_properties) {
@@ -1395,16 +1445,6 @@ void PrerenderLocalPredictor::IssuePrerender(
       new_prerender_handle->OnCancel();
       RecordEvent(EVENT_ISSUE_PRERENDER_CANCELLED_OLD_PRERENDER);
     }
-    // If we are prefetching rather than prerendering, now is the time to launch
-    // the prefetch.
-    if (IsLocalPredictorPrerenderPrefetchEnabled()) {
-      // Obtain the render frame host that caused this prefetch.
-      RenderFrameHost* rfh = RenderFrameHost::FromID(info->render_process_id_,
-                                                     info->render_frame_id_);
-      // If it is still alive, launch the prefresh.
-      if (rfh)
-        rfh->Send(new PrefetchMsg_Prefetch(rfh->GetRoutingID(), url));
-    }
   }
 
   RecordEvent(EVENT_ADD_VISIT_PRERENDERING);