Add implementation for Ad Networks Database

chrome/browser/extensions/activity_log/ad_network_database.h

 // Copyright 2014 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 CHROME_BROWSER_EXTENSIONS_ACTIVITY_LOG_AD_NETWORK_DATABASE_H_
 #define CHROME_BROWSER_EXTENSIONS_ACTIVITY_LOG_AD_NETWORK_DATABASE_H_
 
 #include "base/memory/scoped_ptr.h"
 
 class GURL;
 
 namespace extensions {
 class Action;
 
 // A database of ad networks.
 class AdNetworkDatabase {
  public:
   virtual ~AdNetworkDatabase();
 
   static const AdNetworkDatabase* Get();
   static void SetForTesting(scoped_ptr<AdNetworkDatabase> database);
 
+  // Returns true if the url is in the list of known ad networks.
   virtual bool IsAdNetwork(const GURL& url) const = 0;
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_ACTIVITY_LOG_AD_NETWORK_DATABASE_H_