Reland: Explicitly track the scheduler task enqueueing order in a new field

components/scheduler/child/task_queue_manager.h

Index: components/scheduler/child/task_queue_manager.h
diff --git a/components/scheduler/child/task_queue_manager.h b/components/scheduler/child/task_queue_manager.h
index 8a78dc5ad30b70690179159b53413e2f3cb69b47..5fb88648e4dcc42c7ce40166404079683401f1fc 100644
--- a/components/scheduler/child/task_queue_manager.h
+++ b/components/scheduler/child/task_queue_manager.h
@@ -31,6 +31,7 @@ class TracedValue;
 namespace scheduler {
 namespace internal {
 class LazyNow;
+struct SchedulerTask;
 class TaskQueueImpl;
 }  // namespace internal
 
@@ -103,7 +104,7 @@ class SCHEDULER_EXPORT TaskQueueManager
   void OnTaskQueueEnabled() override;
 
   // Called by the task queue to register a new pending task.
-  void DidQueueTask(const base::PendingTask& pending_task);
+  void DidQueueTask(internal::SchedulerTask& pending_task);

[Sami, 2015/08/05 11:27:34]

The argument should be a pointer since we're modifying it.

[alex clarke (OOO till 29th), 2015/08/05 14:32:44]

Done.

 
   // Post a task to call DoWork() on the main task runner.  Only one pending
   // DoWork is allowed from the main thread, to prevent an explosion of pending
@@ -119,7 +120,7 @@ class SCHEDULER_EXPORT TaskQueueManager
   // run and |should_trigger_wakeup|. Call with an empty |previous_task| if no
   // task was just run.
   void UpdateWorkQueues(bool should_trigger_wakeup,
-                        const base::PendingTask* previous_task);
+                        const internal::SchedulerTask* previous_task);
 
   // Chooses the next work queue to service. Returns true if |out_queue|
   // indicates the queue from which the next task should be run, false to
@@ -131,7 +132,7 @@ class SCHEDULER_EXPORT TaskQueueManager
   // run loop. The queue must not be empty. Returns true if the TaskQueueManager
   // got deleted, and false otherwise.
   bool ProcessTaskFromWorkQueue(internal::TaskQueueImpl* queue,
-                                base::PendingTask* out_previous_task);
+                                internal::SchedulerTask* out_previous_task);
 
   bool RunsTasksOnCurrentThread() const;
   bool PostDelayedTask(const tracked_objects::Location& from_here,
@@ -144,6 +145,7 @@ class SCHEDULER_EXPORT TaskQueueManager
   base::TimeTicks Now() const;
 
   int GetNextSequenceNumber();
+  int GetNextAgeNumber();
 
   scoped_refptr<base::trace_event::ConvertableToTraceFormat>
   AsValueWithSelectorResult(bool should_run,
@@ -169,6 +171,7 @@ class SCHEDULER_EXPORT TaskQueueManager
   std::set<internal::TaskQueueImpl*> updatable_queue_set_;
 
   base::AtomicSequenceNumber task_sequence_num_;
+  base::AtomicSequenceNumber task_age_num_;
   base::debug::TaskAnnotator task_annotator_;
 
   base::ThreadChecker main_thread_checker_;