Track task ids for navigations cross multiple tabs.

components/sync_sessions/task_tracker.cc

Index: components/sync_sessions/task_tracker.cc
diff --git a/components/sync_sessions/task_tracker.cc b/components/sync_sessions/task_tracker.cc
index 0f8902e2905383a98113746e138927b4909e1d7c..6eb618e108585c70b2969a2a88e8d01d9a92c3ed 100644
--- a/components/sync_sessions/task_tracker.cc
+++ b/components/sync_sessions/task_tracker.cc
@@ -17,6 +17,13 @@ int kMaxNumTasksPerTab = 100;
 
 TabTasks::TabTasks() {}
 
+TabTasks::TabTasks(const TabTasks* source_tab) {
+  if (source_tab->current_navigation_index_ >= 0) {
+    source_tab_task_ids_ = source_tab->GetTaskIdsForNavigation(
+        source_tab->current_navigation_index_);
+  }
+}
+
 TabTasks::~TabTasks() {}
 
 std::vector<int64_t> TabTasks::GetTaskIdsForNavigation(
@@ -44,6 +51,20 @@ std::vector<int64_t> TabTasks::GetTaskIdsForNavigation(
       task_id_and_root.root_navigation_index > excluded_navigation_num_
           ? task_id_and_root.root_navigation_index - excluded_navigation_num_
           : 0;
+  // Only consider tasks from source tab when no tasks in current tab is
+  // excluded because max number per tab limit.
+  if (excluded_navigation_num_ == 0) {
+    int first_task_of_tab_position = 0;
+    // skipping invalid heading tasks
+    for (; first_task_of_tab_position < navigation_position &&
+           task_ids_[first_task_of_tab_position].root_navigation_index < 0;
+         first_task_of_tab_position++) {
+    }
+    // If task of current navigation can track back to the first task of the
+    // tab, then consider the source tab.
+    if (task_id_and_root.root_navigation_index == first_task_of_tab_position)
+      root_to_self_task_ids = source_tab_task_ids_;
+  }
   for (int i = root_navigation_index; i <= navigation_position; i++) {
     // Fills the vector with valid tasks.
     if (task_ids_[i].root_navigation_index >= 0)
@@ -163,6 +184,20 @@ TabTasks* TaskTracker::GetTabTasks(SessionID::id_type tab_id) {
   return local_tab_tasks_map_[tab_id].get();
 }
 
+TabTasks* TaskTracker::GetTabTasks(SessionID::id_type tab_id,
+                                   SessionID::id_type source_tab_id) {
+  if (local_tab_tasks_map_.find(tab_id) == local_tab_tasks_map_.end()) {
+    auto iter = local_tab_tasks_map_.find(source_tab_id);
+    if (iter != local_tab_tasks_map_.end()) {
+      local_tab_tasks_map_[tab_id] =
+          base::MakeUnique<TabTasks>(iter->second.get());
+    } else {
+      local_tab_tasks_map_[tab_id] = base::MakeUnique<TabTasks>();
+    }
+  }
+  return local_tab_tasks_map_[tab_id].get();
+}
+
 void TaskTracker::CleanTabTasks(SessionID::id_type tab_id) {
   auto iter = local_tab_tasks_map_.find(tab_id);
   if (iter != local_tab_tasks_map_.end()) {