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

components/history/core/browser/history_backend.h

 // Copyright (c) 2012 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 COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_BACKEND_H_
 #define COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_BACKEND_H_
 
 #include <set>
 #include <string>
 #include <utility>
@@ skipping 256 matching lines @@
                             MostVisitedURLList* result);
 
   // Request the |result_count| URLs and the chain of redirects
   // leading to each of these URLs, filterd and sorted based on the |filter|.
   // If |debug| is enabled, additional data will be computed and provided.
   void QueryFilteredURLs(int result_count,
                          const VisitFilter& filter,
                          bool debug,
                          FilteredURLList* result);
 
+  // Statistics ----------------------------------------------------------------
+
+  // Count the number of URLs in the browsing history.

[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.

+  HistoryCountResult GetHistoryCount();
+
   // Favicon -------------------------------------------------------------------
 
   void GetFavicons(
       const std::vector<GURL>& icon_urls,
       int icon_types,
       const std::vector<int>& desired_sizes,
       std::vector<favicon_base::FaviconRawBitmapResult>* bitmap_results);
 
   void GetLargestFaviconForURL(
       const GURL& page_url,
@@ skipping 593 matching lines @@
 
   // List of observers
   base::ObserverList<HistoryBackendObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(HistoryBackend);
 };
 
 }  // namespace history
 
 #endif  // COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_BACKEND_H_