Only record the execution time during startup.

chrome/browser/history/top_sites_impl.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/history/top_sites_impl.h"
 
 #include <algorithm>
 #include <set>
 
 #include "base/bind.h"
@@ skipping 607 matching lines @@
     new_url.redirects.push_back(url);
   }
   new_url.last_forced_time = time;
   // Add forced URLs and sort. Added to the end of the list of forced URLs
   // since this is almost always where it needs to go, unless the user's local
   // clock is fiddled with.
   MostVisitedURLList::iterator mid = new_list.begin() + num_forced;
   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;
 }
 
 bool TopSitesImpl::AddPrepopulatedPages(MostVisitedURLList* urls,
                                         size_t num_forced_urls) {
   bool added = false;
   for (const auto& prepopulated_page : prepopulated_pages_) {
     if (urls->size() - num_forced_urls < kNonForcedTopSitesNumber &&
         IndexOf(*urls, prepopulated_page.most_visited.url) == -1) {
       urls->push_back(prepopulated_page.most_visited);
@@ skipping 106 matching lines @@
         return;
       const GURL& url = load_details->entry->GetURL();
       if (!cache_->IsKnownURL(url) && CanAddURLToHistory(url)) {
         // To avoid slamming history we throttle requests when the url updates.
         // To do otherwise negatively impacts perf tests.
         RestartQueryForTopSitesTimer(GetUpdateDelay());
       }
     }
 }
 
-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);
   size_t num_forced_urls = MergeCachedForcedURLs(&top_sites);
   AddPrepopulatedPages(&top_sites, num_forced_urls);
 
   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();
 
   // We always do the following steps (setting top sites in cache, and resetting
   // thread safe cache ...) as this method is invoked during startup at which
   // point the caches haven't been updated yet.
   cache_->SetTopSites(top_sites);
 
   // See if we have any tmp thumbnails for the new sites.
@@ skipping 96 matching lines @@
   timer_.Start(FROM_HERE, delta, this, &TopSitesImpl::TimerFired);
 }
 
 void TopSitesImpl::OnGotMostVisitedThumbnails(
     const scoped_refptr<MostVisitedThumbnails>& thumbnails) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   // 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();
 
   MoveStateToLoaded();
 
   // Start a timer that refreshes top sites from history.
   RestartQueryForTopSitesTimer(
       base::TimeDelta::FromSeconds(kUpdateIntervalSecs));
 }
 
 void TopSitesImpl::OnTopSitesAvailableFromHistory(
     const MostVisitedURLList* pages) {
   DCHECK(pages);
-  SetTopSites(*pages);
+  SetTopSites(*pages, TopSitesBackend::fomOtherPlaces);
 }
 
 void TopSitesImpl::OnURLsDeleted(HistoryService* history_service,
                                  bool all_history,
                                  bool expired,
                                  const URLRows& deleted_rows,
                                  const std::set<GURL>& favicon_urls) {
   if (!loaded_)
     return;
 
   if (all_history) {
-    SetTopSites(MostVisitedURLList());
+    SetTopSites(MostVisitedURLList(), TopSitesBackend::fomOtherPlaces);
     backend_->ResetDatabase();
   } else {
     std::set<size_t> indices_to_delete;  // Indices into top_sites_.
     for (const auto& row : deleted_rows) {
       if (cache_->IsKnownURL(row.url()))
         indices_to_delete.insert(cache_->GetURLIndex(row.url()));
     }
 
     if (indices_to_delete.empty())
       return;
 
     MostVisitedURLList new_top_sites(cache_->top_sites());
     for (std::set<size_t>::reverse_iterator i = indices_to_delete.rbegin();
          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();
 }
 
 void TopSitesImpl::HistoryServiceBeingDeleted(HistoryService* history_service) {
   history_service_observer_.Remove(history_service);
 }
 
 }  // namespace history