Add History.TopHostsVisitsByRank UMA metric.

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>
 #include <vector>
 
+#include "base/containers/hash_tables.h"
 #include "base/containers/mru_cache.h"
 #include "base/files/file_path.h"
 #include "base/gtest_prod_util.h"
 #include "base/memory/memory_pressure_listener.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/observer_list.h"
 #include "base/single_thread_task_runner.h"
 #include "base/supports_user_data.h"
 #include "base/task/cancelable_task_tracker.h"
 #include "components/favicon_base/favicon_usage_data.h"
@@ skipping 171 matching lines @@
   // Persists any in-flight state, without actually shutting down the history
   // system. This is intended for use when the application is backgrounded.
   void PersistState();
 #endif
 
   void ClearCachedDataForContextID(ContextID context_id);
 
   // Computes the |num_hosts| most-visited hostnames in the past 30 days. See
   // history_service.h for details. Returns an empty list if db_ is not
   // initialized.
+  //
+  // As a side effect, caches the list of top hosts for the purposes of
+  // generating internal metrics.
   TopHostsList TopHosts(int num_hosts) const;
 
   // Navigation ----------------------------------------------------------------
 
   // |request.time| must be unique with high probability.
   void AddPage(const HistoryAddPageArgs& request);
   virtual void SetPageTitle(const GURL& url, const base::string16& title);
   void AddPageNoVisitForBookmark(const GURL& url, const base::string16& title);
   void UpdateWithPageEndTime(ContextID context_id,
                              int nav_entry_id,
@@ skipping 506 matching lines @@
   void NotifyURLVisited(ui::PageTransition transition,
                         const URLRow& row,
                         const RedirectList& redirects,
                         base::Time visit_time) override;
   void NotifyURLsModified(const URLRows& rows) override;
   void NotifyURLsDeleted(bool all_history,
                          bool expired,
                          const URLRows& rows,
                          const std::set<GURL>& favicon_urls) override;
 
+  void RecordTopHostsMetrics(const GURL& url);
+
   // Deleting all history ------------------------------------------------------
 
   // Deletes all history. This is a special case of deleting that is separated
   // from our normal dependency-following method for performance reasons. The
   // logic lives here instead of ExpireHistoryBackend since it will cause
   // re-initialization of some databases (e.g. Thumbnails) that could fail.
   // When these databases are not valid, our pointers must be null, so we need
   // to handle this type of operation to keep the pointers in sync.
   void DeleteAllHistory();
 
@@ skipping 85 matching lines @@
   // of inheritance from base::SupportsUserData).
   scoped_ptr<HistoryBackendHelper> supports_user_data_helper_;
 
   // Used to manage syncing of the typed urls datatype. This will be null before
   // Init is called.
   scoped_ptr<TypedUrlSyncableService> typed_url_syncable_service_;
 
   // Listens for the system being under memory pressure.
   scoped_ptr<base::MemoryPressureListener> memory_pressure_listener_;
 
+  // Map from host to 1-based index in the TopHosts list.
+  mutable base::hash_map<std::string, int> host_ranks_;
+
   // List of observers
   base::ObserverList<HistoryBackendObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(HistoryBackend);
 };
 
 }  // namespace history
 
 #endif  // COMPONENTS_HISTORY_CORE_BROWSER_HISTORY_BACKEND_H_