Only record the execution time during startup.

chrome/browser/history/top_sites_impl.cc

Index: chrome/browser/history/top_sites_impl.cc
diff --git a/chrome/browser/history/top_sites_impl.cc b/chrome/browser/history/top_sites_impl.cc
index 2cad9e33fbef645cfcc91427f0957dfaae3cf286..306505904f0787abc89a84325f22c3662ef690cd 100644
--- a/chrome/browser/history/top_sites_impl.cc
+++ b/chrome/browser/history/top_sites_impl.cc
@@ -625,7 +625,7 @@ bool TopSitesImpl::AddForcedURL(const GURL& url, const base::Time& time) {
   new_list.insert(mid, new_url);
   mid = new_list.begin() + num_forced;  // Mid was invalidated.
   std::inplace_merge(new_list.begin(), mid, mid + 1, ForcedURLComparator);
-  SetTopSites(new_list);
+  SetTopSites(new_list, TopSitesBackend::CALL_LOCATION_FROM_OTHER_PLACES);
   return true;
 }
 
@@ -752,7 +752,9 @@ void TopSitesImpl::Observe(int type,
     }
 }
 
-void TopSitesImpl::SetTopSites(const MostVisitedURLList& new_top_sites) {
+void TopSitesImpl::SetTopSites(
+    const MostVisitedURLList& new_top_sites,
+    const TopSitesBackend::CallLocation location) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   MostVisitedURLList top_sites(new_top_sites);
@@ -761,8 +763,25 @@ void TopSitesImpl::SetTopSites(const MostVisitedURLList& new_top_sites) {
 
   TopSitesDelta delta;
   DiffMostVisited(cache_->top_sites(), top_sites, &delta);
+
+  // Record the delta size into a histogram if this function is called from
+  // function OnGotMostVisitedThumbnails and no histogram value has been
+  // recorded before.
+  if (location ==
+      TopSitesBackend::CALL_LOCATION_FROM_ON_GOT_MOST_VISITED_THUMBNAILS &&
+      backend_->histogram_recorded() ==
+      TopSitesBackend::HISTOGRAM_RECORDING_NOT_YET) {
+    size_t delta_size =
+        delta.deleted.size() + delta.added.size() + delta.moved.size();
+    UMA_HISTOGRAM_COUNTS_100(
+        "History.UpdateTopSitesOnDBThread_Startup_DeltaSize", delta_size);
+    // Increase the enum value so that TopSitesBackend knows that it should
+    // record the relevant histogram value as well.
+    backend_->IncraseHistogramRecordingStatus();
+  }
+
   if (!delta.deleted.empty() || !delta.added.empty() || !delta.moved.empty()) {
-    backend_->UpdateTopSites(delta);
+    backend_->UpdateTopSites(delta, location);
   }
 
   last_num_urls_changed_ = delta.added.size() + delta.moved.size();
@@ -879,7 +898,9 @@ void TopSitesImpl::OnGotMostVisitedThumbnails(
   // Set the top sites directly in the cache so that SetTopSites diffs
   // correctly.
   cache_->SetTopSites(thumbnails->most_visited);
-  SetTopSites(thumbnails->most_visited);
+  SetTopSites(
+      thumbnails->most_visited,
+      TopSitesBackend::CALL_LOCATION_FROM_ON_GOT_MOST_VISITED_THUMBNAILS);
   cache_->SetThumbnails(thumbnails->url_to_images_map);
 
   ResetThreadSafeImageCache();
@@ -894,7 +915,7 @@ void TopSitesImpl::OnGotMostVisitedThumbnails(
 void TopSitesImpl::OnTopSitesAvailableFromHistory(
     const MostVisitedURLList* pages) {
   DCHECK(pages);
-  SetTopSites(*pages);
+  SetTopSites(*pages, TopSitesBackend::CALL_LOCATION_FROM_OTHER_PLACES);
 }
 
 void TopSitesImpl::OnURLsDeleted(HistoryService* history_service,
@@ -906,7 +927,8 @@ void TopSitesImpl::OnURLsDeleted(HistoryService* history_service,
     return;
 
   if (all_history) {
-    SetTopSites(MostVisitedURLList());
+    SetTopSites(MostVisitedURLList(),
+                TopSitesBackend::CALL_LOCATION_FROM_OTHER_PLACES);
     backend_->ResetDatabase();
   } else {
     std::set<size_t> indices_to_delete;  // Indices into top_sites_.
@@ -923,7 +945,8 @@ void TopSitesImpl::OnURLsDeleted(HistoryService* history_service,
          i != indices_to_delete.rend(); i++) {
       new_top_sites.erase(new_top_sites.begin() + *i);
     }
-    SetTopSites(new_top_sites);
+    SetTopSites(new_top_sites,
+                TopSitesBackend::CALL_LOCATION_FROM_OTHER_PLACES);
   }
   StartQueryForMostVisited();
 }