Sync: Handle duplicating tab IDs in foreign session data

chrome/browser/sync/sessions/sessions_sync_manager.cc

 // 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.
 
 #include "chrome/browser/sync/sessions/sessions_sync_manager.h"
 
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/sync/glue/synced_tab_delegate.h"
 #include "chrome/browser/sync/glue/synced_window_delegate.h"
@@ skipping 634 matching lines @@
       BuildSyncedSessionFromSpecifics(foreign_session_tag,
                                       window_s,
                                       modification_time,
                                       foreign_session->windows[window_id]);
     }
     // Delete any closed windows and unused tabs as necessary.
     session_tracker_.CleanupSession(foreign_session_tag);
   } else if (specifics.has_tab()) {
     const sync_pb::SessionTab& tab_s = specifics.tab();
     SessionID::id_type tab_id = tab_s.tab_id();
+
+    const SessionTab* existing_tab;
+    if (session_tracker_.LookupSessionTab(
+            foreign_session_tag, tab_id, &existing_tab) &&
+        existing_tab->timestamp > modification_time) {
+      DVLOG(1) << "Ignoring " << foreign_session_tag << "'s session tab "
+               << tab_id << " with earlier modification time";
+      return;
+    }
+
     SessionTab* tab =
         session_tracker_.GetTab(foreign_session_tag,
                                 tab_id,
                                 specifics.tab_node_id());
 
     // Update SessionTab based on protobuf.
     tab->SetFromSyncData(tab_s, modification_time);
 
     // If a favicon or favicon urls are present, load the URLs and visit
     // times into the in-memory favicon cache.
@@ skipping 374 matching lines @@
                << " with age " << session_age_in_days << ", deleting.";
       DeleteForeignSessionInternal(session_tag, &changes);
     }
   }
 
   if (!changes.empty())
     sync_processor_->ProcessSyncChanges(FROM_HERE, changes);
 }
 
 };  // namespace browser_sync