Only record the execution time during startup.

components/history/core/browser/top_sites_backend.h

Index: components/history/core/browser/top_sites_backend.h
diff --git a/components/history/core/browser/top_sites_backend.h b/components/history/core/browser/top_sites_backend.h
index d3c054b81032026a27077b0837323c028fba7eaf..b10a73e9ff2bcf5d9bcd285cb38002ea09d11e46 100644
--- a/components/history/core/browser/top_sites_backend.h
+++ b/components/history/core/browser/top_sites_backend.h
@@ -26,6 +26,22 @@ class TopSitesDatabase;
 // thread.
 class TopSitesBackend : public base::RefCountedThreadSafe<TopSitesBackend> {
  public:
+  // An enum representing different situations under which function
+  // TopSitesImpl::SetTopSites and TopSitesBackend::UpdateTopSites can be
+  // initiated.
+  // This is needed because a histogram is used to record speed related metrics
+  // when TopSitesImpl::SetTopSites and TopSitesBackend::UpdateTopSites are
+  // initiated from TopSitesImpl::OnGotMostVisitedThumbnails, which usually
+  // happens early and might affect Chrome startup speed.
+  // TODO(yiyaoliu): Remove this when crbug/223430 is fixed.
+  enum TopSitesCalledLocation {

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

This is in the topsites files, so prefixing with topsites just makes this more
verbose. How about CallLocation

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

Done.

+    // SetTopSites is called when MostVisitedThumbnails is available (function
+    // TopSitesImpl::OnGotMostVisitedThumbnails).
+    fromOnGotMostVisitedThumbnails,

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

Style guide says enums are ALL_CAPS. And generally we prefix with name of enum,
eg CALL_LOCATION_FROM_ON_GOT_MOST_VISITED_THUMBNAILS.

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

Done.

+    // All other situations.
+    fomOtherPlaces
+  };
+
   // The boolean parameter indicates if the DB existed on disk or needs to be
   // migrated.
   typedef base::Callback<void(const scoped_refptr<MostVisitedThumbnails>&)>
@@ -45,7 +61,9 @@ class TopSitesBackend : public base::RefCountedThreadSafe<TopSitesBackend> {
       base::CancelableTaskTracker* tracker);
 
   // Updates top sites database from the specified delta.
-  void UpdateTopSites(const TopSitesDelta& delta);
+  // TODO(yiyaoliu): Remove the 2nd parameter when crbug/223430 is fixed.
+  void UpdateTopSites(const TopSitesDelta& delta,
+                      const TopSitesCalledLocation location);
 
   // Sets the thumbnail.
   void SetPageThumbnail(const MostVisitedURL& url,
@@ -77,7 +95,9 @@ class TopSitesBackend : public base::RefCountedThreadSafe<TopSitesBackend> {
       scoped_refptr<MostVisitedThumbnails> thumbnails);
 
   // Updates top sites.
-  void UpdateTopSitesOnDBThread(const TopSitesDelta& delta);
+  // TODO(yiyaoliu): Remove the 2nd parameter when crbug/223430 is fixed.
+  void UpdateTopSitesOnDBThread(const TopSitesDelta& delta,
+                                const TopSitesCalledLocation location);
 
   // Sets the thumbnail.
   void SetPageThumbnailOnDBThread(const MostVisitedURL& url,