[Sync] Handle reassociation of tabs where the old tab is already mapped.

components/sync_sessions/sessions_sync_manager_unittest.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 "components/sync_sessions/sessions_sync_manager.h"
 
 #include <stdint.h>
 
 #include <utility>
 
@@ skipping 1677 matching lines @@
                                                       &tab_node_ids);
   EXPECT_EQ(1U, tab_node_ids.size());
   EXPECT_TRUE(tab_node_ids.find(tab_node_id_unique) != tab_node_ids.end());
 
   manager()->DoGarbageCollection();
   EXPECT_EQ(1U, output.size());
 }
 
 TEST_F(SessionsSyncManagerTest, AssociationReusesNodes) {
   SyncChangeList changes;
-  AddTab(AddWindow()->GetSessionId(), kFoo1);
+  TestSyncedWindowDelegate* window = AddWindow();
+  TestSyncedTabDelegate* tab = AddTab(window->GetSessionId(), kFoo1);
   InitWithSyncDataTakeOutput(SyncDataList(), &changes);
   ASSERT_TRUE(ChangeTypeMatches(changes,
                                 {SyncChange::ACTION_ADD, SyncChange::ACTION_ADD,
                                  SyncChange::ACTION_UPDATE}));
   ASSERT_TRUE(changes[1].sync_data().GetSpecifics().session().has_tab());
   int tab_node_id =
       changes[1].sync_data().GetSpecifics().session().tab_node_id();
 
   // Pass back the previous tab and header nodes at association, along with a
   // second tab node (with a rewritten tab node id).
@@ skipping 12 matching lines @@
   manager()->StopSyncing(syncer::SESSIONS);
   InitWithSyncDataTakeOutput(in, &changes);
 
   // No tab entities should be deleted. The original (lower) tab node id should
   // be reused for association.
   FilterOutLocalHeaderChanges(&changes);
   ASSERT_TRUE(ChangeTypeMatches(changes, {SyncChange::ACTION_UPDATE}));
   VerifyLocalTabChange(changes[0], 1, kFoo1);
   EXPECT_EQ(tab_node_id,
             changes[0].sync_data().GetSpecifics().session().tab_node_id());
+  changes.clear();
+
+  // Update the original tab. Ensure the same tab node is updated.
+  NavigateTab(tab, kFoo2);
+  FilterOutLocalHeaderChanges(&changes);
+  ASSERT_TRUE(ChangeTypeMatches(changes, {SyncChange::ACTION_UPDATE}));
+  VerifyLocalTabChange(changes[0], 2, kFoo2);
+  EXPECT_EQ(tab_node_id,
+            changes[0].sync_data().GetSpecifics().session().tab_node_id());
+  changes.clear();
+
+  // Add a new tab. It should reuse the second tab node.
+  AddTab(window->GetSessionId(), kBar1);
+  FilterOutLocalHeaderChanges(&changes);
+  ASSERT_TRUE(ChangeTypeMatches(changes, {SyncChange::ACTION_UPDATE}));
+  VerifyLocalTabChange(changes[0], 1, kBar1);
+  EXPECT_EQ(tab_node_id + 1,
+            changes[0].sync_data().GetSpecifics().session().tab_node_id());
 }
 
 // Ensure that the merge process deletes a tab node without a tab id.
 TEST_F(SessionsSyncManagerTest, MergeDeletesTabMissingTabId) {
   SyncChangeList changes;
   InitWithNoSyncData();
 
   std::string local_tag = manager()->current_machine_tag();
   int tab_node_id = 0;
   sync_pb::SessionSpecifics specifics;
@@ skipping 847 matching lines @@
   EXPECT_EQ(tab.navigation_size(), 2);
   EXPECT_EQ(tab.navigation(0).global_id(), tab.navigation(0).task_id());
   EXPECT_TRUE(tab.navigation(0).ancestor_task_id().empty());
   EXPECT_EQ(tab.navigation(1).global_id(), tab.navigation(1).task_id());
   // navigation(1) is a subtask of navigation(0).
   EXPECT_EQ(tab.navigation(1).ancestor_task_id_size(), 1);
   EXPECT_EQ(tab.navigation(1).ancestor_task_id(0), tab.navigation(0).task_id());
 }
 
 }  // namespace sync_sessions