Only record the execution time during startup.

components/history/core/browser/top_sites_backend.cc

 // Copyright (c) 2011 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 "components/history/core/browser/top_sites_backend.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/files/file_path.h"
 #include "base/location.h"
@@ skipping 29 matching lines @@
     const GetMostVisitedThumbnailsCallback& callback,
     base::CancelableTaskTracker* tracker) {
   scoped_refptr<MostVisitedThumbnails> thumbnails = new MostVisitedThumbnails();
   tracker->PostTaskAndReply(
       db_task_runner_.get(), FROM_HERE,
       base::Bind(&TopSitesBackend::GetMostVisitedThumbnailsOnDBThread, this,
                  thumbnails),
       base::Bind(callback, thumbnails));
 }
 
-void TopSitesBackend::UpdateTopSites(const TopSitesDelta& delta) {
+void TopSitesBackend::UpdateTopSites(const TopSitesDelta& delta, bool startup) {
   db_task_runner_->PostTask(
       FROM_HERE,
-      base::Bind(&TopSitesBackend::UpdateTopSitesOnDBThread, this, delta));
+      base::Bind(&TopSitesBackend::UpdateTopSitesOnDBThread, this, delta,
+                 startup));
 }
 
 void TopSitesBackend::SetPageThumbnail(const MostVisitedURL& url,
                                        int url_rank,
                                        const Images& thumbnail) {
   db_task_runner_->PostTask(
       FROM_HERE, base::Bind(&TopSitesBackend::SetPageThumbnailOnDBThread, this,
                             url, url_rank, thumbnail));
 }
 
@@ skipping 30 matching lines @@
 void TopSitesBackend::GetMostVisitedThumbnailsOnDBThread(
     scoped_refptr<MostVisitedThumbnails> thumbnails) {
   DCHECK(db_task_runner_->BelongsToCurrentThread());
 
   if (db_) {
     db_->GetPageThumbnails(&(thumbnails->most_visited),
                            &(thumbnails->url_to_images_map));
   }
 }
 
-void TopSitesBackend::UpdateTopSitesOnDBThread(const TopSitesDelta& delta) {
+void TopSitesBackend::UpdateTopSitesOnDBThread(const TopSitesDelta& delta,
+                                               bool startup) {
   TRACE_EVENT0("startup", "history::TopSitesBackend::UpdateTopSitesOnDBThread");
 
   if (!db_)
     return;
 
   // TODO(yiyaoliu): Remove the histogram and related code when crbug/223430 is
   // fixed.
   base::TimeTicks begin_time = base::TimeTicks::Now();
 
   for (size_t i = 0; i < delta.deleted.size(); ++i)
     db_->RemoveURL(delta.deleted[i]);
 
   for (size_t i = 0; i < delta.added.size(); ++i)
     db_->SetPageThumbnail(delta.added[i].url, delta.added[i].rank, Images());
 
   for (size_t i = 0; i < delta.moved.size(); ++i)
     db_->UpdatePageRank(delta.moved[i].url, delta.moved[i].rank);
 
-  UMA_HISTOGRAM_TIMES("History.UpdateTopSitesOnDBThreadTime",
-                      base::TimeTicks::Now() - begin_time);
+  if (startup) {
+    UMA_HISTOGRAM_TIMES("History.UpdateTopSitesOnDBThread_Startup_Time",

[sky, 2015/03/31 23:58:49]

Didn't you want to put the size of delta in the name?

[yao, 2015/04/01 21:43:00]

The delta size is recorded in TopSitesImpl::SetTopSites, so that the delta size
is also recorded when it's 0. This way we know what percentage of times delta is
zero/not zero. 

+                        base::TimeTicks::Now() - begin_time);
+  }
 }
 
 void TopSitesBackend::SetPageThumbnailOnDBThread(const MostVisitedURL& url,
                                                  int url_rank,
                                                  const Images& thumbnail) {
   if (!db_)
     return;
 
   db_->SetPageThumbnail(url, url_rank, thumbnail);
 }
 
 void TopSitesBackend::ResetDatabaseOnDBThread(const base::FilePath& file_path) {
   DCHECK(db_task_runner_->BelongsToCurrentThread());
   db_.reset(NULL);
   sql::Connection::Delete(db_path_);
   db_.reset(new TopSitesDatabase());
   InitDBOnDBThread(db_path_);
 }
 
 }  // namespace history