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..7f34470075315c24900de8872048b25f2def8230 100644
--- a/components/history/core/browser/top_sites_backend.h
+++ b/components/history/core/browser/top_sites_backend.h
@@ -26,6 +26,43 @@ class TopSitesDatabase;
 // thread.
 class TopSitesBackend : public base::RefCountedThreadSafe<TopSitesBackend> {
  public:
+  // TODO(yiyaoliu): Remove the enums and related code when crbug/223430 is
+  // fixed.
+
+  // 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.
+  enum CallLocation {
+    // SetTopSites is called when MostVisitedThumbnails is available (function
+    // TopSitesImpl::OnGotMostVisitedThumbnails).
+    CALL_LOCATION_FROM_ON_GOT_MOST_VISITED_THUMBNAILS,
+    // All other situations.
+    CALL_LOCATION_FROM_OTHER_PLACES
+  };
+
+  // An enum representing the histogram recording status used by class
+  // TopSitesImpl and class TopSitesBackend. The purpose is to make sure that
+  // TopSitesImpl and TopSitesBackend records the relevant histograms at most
+  // once during startup.
+  // The initial value will be HISTOGRAM_RECORDING_NOT_YET. TopSitesImpl will
+  // change it to HISTOGRAM_RECORDING_IN_PROGRESS and records a histogram.
+  // TopSitesBackend will only records the value if this enum is
+  // HISTOGRAM_RECORDING_IN_PROGRESS and after that it changes the enum value to
+  // HISTOGRAM_RECORDING_DONE.
+  enum HistogramRecording {
+    HISTOGRAM_RECORDING_NOT_YET,
+    HISTOGRAM_RECORDING_IN_PROGRESS,
+    HISTOGRAM_RECORDING_DONE
+  };
+
+  // Move the histogram recording status to the next step.
+  static void IncraseHistogramRecordingStatus();

[sky, 2015/04/16 16:05:10]

Increase
Why does this need to be public? Doesn't
TopSitesBackend::UpdateTopSitesOnDBThread have enough information to know it can
increase?

+  static HistogramRecording histogram_recorded() { return histogram_recorded_; }
+
   // 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 +82,9 @@ 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 CallLocation location);
 
   // Sets the thumbnail.
   void SetPageThumbnail(const MostVisitedURL& url,
@@ -77,7 +116,9 @@ 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 CallLocation location);
 
   // Sets the thumbnail.
   void SetPageThumbnailOnDBThread(const MostVisitedURL& url,
@@ -92,6 +133,8 @@ class TopSitesBackend : public base::RefCountedThreadSafe<TopSitesBackend> {
   scoped_ptr<TopSitesDatabase> db_;
   scoped_refptr<base::SingleThreadTaskRunner> db_task_runner_;
 
+  static HistogramRecording histogram_recorded_;
+
   DISALLOW_COPY_AND_ASSIGN(TopSitesBackend);
 };