Use main frame URL to identify referrer if sub-frame url is not available

chrome/browser/safe_browsing/safe_browsing_navigation_observer_manager.h

 // Copyright 2016 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_SAFE_BROWSING_SAFE_BROWSING_NAVIGATION_OBSERVER_MANAGER_H_
 #define CHROME_BROWSER_SAFE_BROWSING_SAFE_BROWSING_NAVIGATION_OBSERVER_MANAGER_H_
 
 #include "base/feature_list.h"
 #include "chrome/common/safe_browsing/csd.pb.h"
 #include "content/public/browser/notification_observer.h"
@@ skipping 138 matching lines @@
   // delayed download in Window D. Before the download occurs, url2 in window B
   // opens a different about:blank page in window C.
   // A ---- C - D
   //   \   /
   //     B
   // In this case, FindNavigationEvent() will think url2 in Window B is the
   // referrer of about::blank in Window C since this navigation is more recent.
   // However, it does not prevent us to attribute url1 in Window A as the cause
   // of all these navigations.
   NavigationEvent* FindNavigationEvent(const GURL& target_url,
+                                       const GURL& target_main_frame_url,

[Nathan Parker, 2017/01/04 18:54:51]

Mention this new arg in the comments

[Jialiu Lin, 2017/01/04 21:47:01]

Done.

                                        int target_tab_id);
 
   void AddToReferrerChain(std::vector<ReferrerChainEntry>* referrer_chain,
                           NavigationEvent* nav_event,
                           ReferrerChainEntry::URLType type);
 
   // navigation_map_ keeps track of all the observed navigations. This map is
   // keyed on the resolved request url. In other words, in case of server
   // redirects, its key is the last server redirect url, otherwise, it is the
   // original target url. Since the same url can be requested multiple times
@@ skipping 17 matching lines @@
 
   content::NotificationRegistrar registrar_;
 
   base::OneShotTimer cleanup_timer_;
 
   DISALLOW_COPY_AND_ASSIGN(SafeBrowsingNavigationObserverManager);
 };
 }  // namespace safe_browsing
 
 #endif  // CHROME_BROWSER_SAFE_BROWSING_SAFE_BROWSING_NAVIGATION_OBSERVER_MANAGER_H_