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..645e62c6a3c36138b61b46ddb1dac22802a2efde 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::fomOtherPlaces);
   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::TopSitesCalledLocation location) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   MostVisitedURLList top_sites(new_top_sites);
@@ -762,7 +764,16 @@ void TopSitesImpl::SetTopSites(const MostVisitedURLList& new_top_sites) {
   TopSitesDelta delta;
   DiffMostVisited(cache_->top_sites(), top_sites, &delta);
   if (!delta.deleted.empty() || !delta.added.empty() || !delta.moved.empty()) {
-    backend_->UpdateTopSites(delta);
+    backend_->UpdateTopSites(delta, location);
+  }
+
+  // Record the delta size into a histogram if this function is called from
+  // function OnGotMostVisitedThumbnails.
+  if (location == TopSitesBackend::fromOnGotMostVisitedThumbnails) {
+    size_t delta_size =
+        delta.deleted.size() + delta.added.size() + delta.moved.size();
+    UMA_HISTOGRAM_COUNTS_100(
+        "History.UpdateTopSitesOnDBThread_Startup_DeltaSize", delta_size);

[sky, 2015/04/01 22:51:48]

The name seems to indicate you want this only at startup (same for other
histogram). If you have multiple profiles this'll be hit more than once. If you
want these values only reported once you need to protect against that.

[yao, 2015/04/02 17:20:31]

Right, I guess we could get the number of profiles from ProfileInfoCache to
decide whether to record or not. Is there a better way?

I feel it's not the end of the world if we don't exclude this case, cause having
more than 1 profile is rather rare case. 

WDYT? 

[sky, 2015/04/02 18:22:18]

What about a static?

[yao, 2015/04/02 19:37:30]

Like a static class member, that indicates whether this histogram has been
recorded, to make sure it can only be recorded once? 

   }
 
   last_num_urls_changed_ = delta.added.size() + delta.moved.size();
@@ -879,7 +890,8 @@ 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::fromOnGotMostVisitedThumbnails);
   cache_->SetThumbnails(thumbnails->url_to_images_map);
 
   ResetThreadSafeImageCache();
@@ -894,7 +906,7 @@ void TopSitesImpl::OnGotMostVisitedThumbnails(
 void TopSitesImpl::OnTopSitesAvailableFromHistory(
     const MostVisitedURLList* pages) {
   DCHECK(pages);
-  SetTopSites(*pages);
+  SetTopSites(*pages, TopSitesBackend::fomOtherPlaces);
 }
 
 void TopSitesImpl::OnURLsDeleted(HistoryService* history_service,
@@ -906,7 +918,7 @@ void TopSitesImpl::OnURLsDeleted(HistoryService* history_service,
     return;
 
   if (all_history) {
-    SetTopSites(MostVisitedURLList());
+    SetTopSites(MostVisitedURLList(), TopSitesBackend::fomOtherPlaces);
     backend_->ResetDatabase();
   } else {
     std::set<size_t> indices_to_delete;  // Indices into top_sites_.
@@ -923,7 +935,7 @@ 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::fomOtherPlaces);
   }
   StartQueryForMostVisited();
 }