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

chrome/browser/sync/glue/session_sync_test_helper.cc

 // 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.
 
 #include "chrome/browser/sync/glue/session_sync_test_helper.h"
 
 #include <stddef.h>
 
 #include "base/strings/utf_string_conversions.h"
 #include "components/sync_sessions/synced_session.h"
@@ skipping 80 matching lines @@
                 ui::PAGE_TRANSITION_TYPED);
     }
   }
 }
 
 void SessionSyncTestHelper::BuildTabSpecifics(
     const std::string& tag,
     int window_id,
     int tab_id,
     sync_pb::SessionSpecifics* tab_base) {
+  BuildTabSpecifics(tag, window_id, tab_id, ++max_tab_node_id_, tab_base);
+}
+
+void SessionSyncTestHelper::BuildTabSpecifics(
+    const std::string& tag,
+    int window_id,
+    int tab_id,
+    int tab_node_id,
+    sync_pb::SessionSpecifics* tab_base) {
   tab_base->set_session_tag(tag);
-  tab_base->set_tab_node_id(++max_tab_node_id_);
+  tab_base->set_tab_node_id(tab_node_id);
   sync_pb::SessionTab* tab = tab_base->mutable_tab();
   tab->set_tab_id(tab_id);
   tab->set_tab_visual_index(1);
   tab->set_current_navigation_index(0);
   tab->set_pinned(true);
   tab->set_extension_app_id(kAppId);
   sync_pb::TabNavigation* navigation = tab->add_navigation();
   navigation->set_virtual_url(kVirtualUrl);
   navigation->set_referrer(kReferrer);
   navigation->set_title(kTitle);
@@ skipping 16 matching lines @@
   for (size_t i = 0; i < tab_list.size(); ++i) {
     BuildTabSpecifics(tag, 0, tab_list[i], &tabs1[i]);
   }
 
   if (tabs)
     tabs->swap(tabs1);
   return meta;
 }
 
 }  // namespace browser_sync