Added HistoryService::GetHistoryCount() and helper functions in components/history

components/history/core/browser/history_service.h

Index: components/history/core/browser/history_service.h
diff --git a/components/history/core/browser/history_service.h b/components/history/core/browser/history_service.h
index f197d2bc25d83f65c7c87f2940a416c1a6930cbf..71fda1678d13f8ed2871f74c3383fc4df71f2f0a 100644
--- a/components/history/core/browser/history_service.h
+++ b/components/history/core/browser/history_service.h
@@ -342,6 +342,17 @@ class HistoryService : public syncer::SyncableService, public KeyedService {
       const QueryFilteredURLsCallback& callback,
       base::CancelableTaskTracker* tracker);
 
+  // Statistics ----------------------------------------------------------------
+
+  // Returns the count of URLs in the url database. The argument is the count.

[msramek, 2015/09/14 17:28:16]

I'd suggest omitting this comment. The fact that this is used in
|GetHistoryCount| gives a clear picture what this callback is for.

Furthermore, count = 0 does not indicate database failure, but success = false
does. You could add that to the |GetHistoryCount| comment.

[lwchkg, 2015/09/15 14:27:08]

Thanks. Just forgot to update the comment here.

+  // The count is zero if query to the database failed.
+  typedef base::Callback<void(HistoryCountResult)> GetHistoryCountCallback;

[msramek, 2015/09/14 17:28:16]

This shouldn't be called "Get", as it's not a getter.

[lwchkg, 2015/09/15 14:27:08]

Puzzled here. This is the callback function in GetHistoryCount, so it's called
GetHistoryCountCallback according the the naming conventions in this file.

[msramek, 2015/09/16 11:16:30]

Oh... of course :) Sorry for that.

+
+  // Returns the count of URLs in the url database.

[msramek, 2015/09/14 17:28:16]

Please update the comment to explain that we're counting distinct URLs per day.

[lwchkg, 2015/09/15 14:27:08]

Acknowledged.

+  base::CancelableTaskTracker::TaskId GetHistoryCount(
+      const GetHistoryCountCallback& callback,
+      base::CancelableTaskTracker* tracker);
+
   // Database management operations --------------------------------------------
 
   // Delete all the information related to a single url.