Only record the execution time during startup.

chrome/browser/history/top_sites_impl.h

Index: chrome/browser/history/top_sites_impl.h
diff --git a/chrome/browser/history/top_sites_impl.h b/chrome/browser/history/top_sites_impl.h
index 91518ec742b6ed79931882101310133b1e8b61cd..827f4985b2f04a909fa1ef2232b5bf044e08d628 100644
--- a/chrome/browser/history/top_sites_impl.h
+++ b/chrome/browser/history/top_sites_impl.h
@@ -195,7 +195,10 @@ class TopSitesImpl : public TopSites,
   // 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