[Sync] Moved tab_node_id tracking to session object and improved foreign session garbage collection.

chrome/browser/sync/glue/session_sync_test_helper.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 CHROME_BROWSER_SYNC_GLUE_SESSION_SYNC_TEST_HELPER_H_
 #define CHROME_BROWSER_SYNC_GLUE_SESSION_SYNC_TEST_HELPER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 19 matching lines @@
 
   static void AddWindowSpecifics(int window_id,
                                  const std::vector<int>& tab_list,
                                  sync_pb::SessionSpecifics* meta);
 
   static void VerifySyncedSession(
       const std::string& tag,
       const std::vector<std::vector<SessionID::id_type>>& windows,
       const sync_driver::SyncedSession& session);
 
+  // Build a SessionSpecifics object with a tab and sample data. Uses a
+  // monotonically increasing variable to generate tab_node_ids and avoid
+  // conflicts.
   void BuildTabSpecifics(const std::string& tag,
                          int window_id,
                          int tab_id,
                          sync_pb::SessionSpecifics* tab_base);
 
+  // Overload of BuildTabSpecifics to allow forcing a specific tab_node_id.
+  // Typically only useful to test reusing tab_node_ids.
+  void BuildTabSpecifics(const std::string& tag,
+                         int window_id,
+                         int tab_id,
+                         int tab_node_id,
+                         sync_pb::SessionSpecifics* tab_base);
+
   sync_pb::SessionSpecifics BuildForeignSession(
       const std::string& tag,
       const std::vector<SessionID::id_type>& tab_list,
       std::vector<sync_pb::SessionSpecifics>* tabs);
 
   void Reset();
 
  private:
   int max_tab_node_id_;
 
   DISALLOW_COPY_AND_ASSIGN(SessionSyncTestHelper);
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_GLUE_SESSION_SYNC_TEST_HELPER_H_