Track task ids for navigations cross multiple tabs.

components/sync_sessions/task_tracker.h

Index: components/sync_sessions/task_tracker.h
diff --git a/components/sync_sessions/task_tracker.h b/components/sync_sessions/task_tracker.h
index 44ee36368a6f879822bf5f8a15dc8cb2878d9d02..3d0e780217c8abba3aff0b078594ce207af699c0 100644
--- a/components/sync_sessions/task_tracker.h
+++ b/components/sync_sessions/task_tracker.h
@@ -29,10 +29,10 @@ namespace sync_sessions {
 // TODO(shenchao): If the tab is restored, then the input navigation is not
 // necessarily the first navigation in this case. Need to fix it by initalizing
 // the object with restored data.
-// TODO(shenchao): Support to track tasks cross tabs.
 class TabTasks {
  public:
   TabTasks();
+  explicit TabTasks(const TabTasks* source_tab);
   virtual ~TabTasks();
 
   // Gets top-down task id list of ancestors and itself for
@@ -67,6 +67,8 @@ class TabTasks {
   // Task ids (with root task) for the navigations of the tab. The vector is
   // corresponding to the sequence of navigations of the tab.
   std::vector<TaskIdAndRoot> task_ids_;
+  // Task ids from the source tab.
+  std::vector<int64_t> source_tab_task_ids_;

[Nicolas Zea, 2017/05/10 00:10:56]

Why store the source tab task in a separate vector? Why not just fill
|task_ids_| with the source tab's tasks?

[shenchao, 2017/05/17 16:48:16]

Done.

   // Index of current navigation in task_ids_.
   int current_navigation_index_ = -1;
   // Number of oldest ancestors which have been excluded from being tracked in
@@ -87,6 +89,11 @@ class TaskTracker {
   // given |tab_id|.
   TabTasks* GetTabTasks(SessionID::id_type tab_id);
 
+  // Returns a TabTasks pointer, which is owned by this object, for the tab of
+  // given |tab_id|, which is created from a source tab |source_tab_id|.
+  TabTasks* GetTabTasks(SessionID::id_type tab_id,
+                        SessionID::id_type source_tab_id);
+
   // Cleans tracked task ids of navigations in the tab of |tab_id|.
   void CleanTabTasks(SessionID::id_type tab_id);