Only record the execution time during startup.

chrome/browser/history/top_sites_impl.h

 // 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.
 
 #ifndef CHROME_BROWSER_HISTORY_TOP_SITES_IMPL_H_
 #define CHROME_BROWSER_HISTORY_TOP_SITES_IMPL_H_
 
 #include <list>
 #include <set>
 #include <string>
@@ skipping 177 matching lines @@
   void Observe(int type,
                const content::NotificationSource& source,
                const content::NotificationDetails& details) override;
 
   // Updates URLs in |cache_| and the db (in the background).
   // The non-forced URLs in |new_top_sites| replace those in |cache_|.
   // The forced URLs of |new_top_sites| are merged with those in |cache_|,
   // if the list of forced URLs overflows, the oldest ones are dropped.
   // All mutations to cache_ *must* go through this. Should
   // be called from the UI thread.
-  void SetTopSites(const MostVisitedURLList& new_top_sites);
+  // The bool param is used for knowing whether this function is called during
+  // startup or not, thus histogram value could be recorded accordingly.
+  // TODO(yiyaoliu): Remove this when crbug/223430 is fixed.
+  void SetTopSites(const MostVisitedURLList& new_top_sites, bool startup);

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

Please use an enum to avoid a mysterious true/false parameter. Also, it's not
startup, it's more of whether this is the call from when history is obtained.

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

I was having debating on the naming of the enum, and also where should the enum
be put. Not sure if this looks good to you. 

 
   // Returns the number of most visited results to request from history. This
   // changes depending upon how many urls have been blacklisted. Should be
   // called from the UI thread.
   int num_results_to_request_from_history() const;
 
   // Invoked when transitioning to LOADED. Notifies any queued up callbacks.
   // Should be called from the UI thread.
   void MoveStateToLoaded();
 
@@ skipping 69 matching lines @@
 
   ScopedObserver<HistoryService, HistoryServiceObserver>
       history_service_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(TopSitesImpl);
 };
 
 }  // namespace history
 
 #endif  // CHROME_BROWSER_HISTORY_TOP_SITES_IMPL_H_