Add UMA Precache.Freshness.Prefetch

components/precache/core/precache_url_table.h

 // Copyright 2013 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_PRECACHE_CORE_PRECACHE_URL_TABLE_H_
 #define COMPONENTS_PRECACHE_CORE_PRECACHE_URL_TABLE_H_
 
 #include <map>
 
 #include "base/macros.h"
 #include "base/time/time.h"
 #include "url/gurl.h"
 
 namespace sql {
 class Connection;
 }
 
 namespace precache {
 
 // Interface for database table that keeps track of the URLs that have been
-// precached but not used. Each row in this table represents a URL that was
-// precached over the network, and has not been fetched through user browsing
-// since then. Manages one table { URL (primary key), precache timestamp }.
+// precached but not used. This table is used to count how many bytes were saved
+// by precached resources.
+// Each row in this table represents a URL that was precached over the network,
+// and has not been fetched through user browsing since then.
+// Manages one table { URL (primary key), precache timestamp }.
 class PrecacheURLTable {
  public:
   PrecacheURLTable();
   ~PrecacheURLTable();
 
   // Initialize the precache URL table for use with the specified database
   // connection. The caller keeps ownership of |db|, and |db| must not be NULL.
   // Init must be called before any other methods.
   bool Init(sql::Connection* db);
 
@@ skipping 21 matching lines @@
 
   // Non-owned pointer.
   sql::Connection* db_;
 
   DISALLOW_COPY_AND_ASSIGN(PrecacheURLTable);
 };
 
 }  // namespace precache
 
 #endif  // COMPONENTS_PRECACHE_CORE_PRECACHE_URL_TABLE_H_