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

components/scheduler/child/task_queue_manager.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/scheduler/child/task_queue_manager.h"
 
 #include <queue>
 #include <set>
 
 #include "base/bind.h"
@@ skipping 86 matching lines @@
 }
 
 void TaskQueueManager::UnregisterAsUpdatableTaskQueue(
     internal::TaskQueueImpl* queue) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   updatable_queue_set_.erase(queue);
 }
 
 void TaskQueueManager::UpdateWorkQueues(
     bool should_trigger_wakeup,
-    const base::PendingTask* previous_task) {
+    const internal::SchedulerTask* previous_task) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   internal::LazyNow lazy_now(this);
 
   // Insert any newly updatable queues into the updatable_queue_set_.
   {
     base::AutoLock lock(newly_updatable_lock_);
     while (!newly_updatable_.empty()) {
       updatable_queue_set_.insert(newly_updatable_.back());
       newly_updatable_.pop_back();
     }
@@ skipping 34 matching lines @@
   if (posted_from_main_thread) {
     pending_dowork_count_--;
     DCHECK_GE(pending_dowork_count_, 0);
   }
   DCHECK(main_thread_checker_.CalledOnValidThread());
 
   // Pass false and nullptr to UpdateWorkQueues here to prevent waking up a
   // pump-after-wakeup queue.
   UpdateWorkQueues(false, nullptr);
 
-  base::PendingTask previous_task((tracked_objects::Location()),
-                                  (base::Closure()));
+  internal::SchedulerTask previous_task;
   for (int i = 0; i < work_batch_size_; i++) {
     internal::TaskQueueImpl* queue;
     if (!SelectQueueToService(&queue))
       return;
     // Note that this function won't post another call to DoWork if one is
     // already pending, so it is safe to call it in a loop.
     MaybePostDoWorkOnMainRunner();
 
     if (ProcessTaskFromWorkQueue(queue, &previous_task))
       return;  // The TaskQueueManager got deleted, we must bail out.
@@ skipping 11 matching lines @@
 
 bool TaskQueueManager::SelectQueueToService(
     internal::TaskQueueImpl** out_queue) {
   bool should_run = selector_.SelectQueueToService(out_queue);
   TRACE_EVENT_OBJECT_SNAPSHOT_WITH_ID(
       disabled_by_default_tracing_category_, "TaskQueueManager", this,
       AsValueWithSelectorResult(should_run, *out_queue));
   return should_run;
 }
 
-void TaskQueueManager::DidQueueTask(const base::PendingTask& pending_task) {
+void TaskQueueManager::DidQueueTask(internal::SchedulerTask& pending_task) {
+  pending_task.sequence_num = GetNextSequenceNumber();
   task_annotator_.DidQueueTask("TaskQueueManager::PostTask", pending_task);
 }
 
 bool TaskQueueManager::ProcessTaskFromWorkQueue(
     internal::TaskQueueImpl* queue,
-    base::PendingTask* out_previous_task) {
+    internal::SchedulerTask* out_previous_task) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   scoped_refptr<DeletionSentinel> protect(deletion_sentinel_);
-  base::PendingTask pending_task = queue->TakeTaskFromWorkQueue();
+  // TODO(alexclarke): consider std::move() when allowed.
+  internal::SchedulerTask pending_task = queue->TakeTaskFromWorkQueue();
 
   if (queue->GetQuiescenceMonitored())
     task_was_run_on_quiescence_monitored_queue_ = true;
 
   if (!pending_task.nestable && main_task_runner_->IsNested()) {
     // Defer non-nestable work to the main task runner.  NOTE these tasks can be
     // arbitrarily delayed so the additional delay should not be a problem.
     main_task_runner_->PostNonNestableTask(pending_task.posted_from,
                                            pending_task.task);
   } else {
@@ skipping 64 matching lines @@
 }
 
 base::TimeTicks TaskQueueManager::Now() const {
   return time_source_->NowTicks();
 }
 
 int TaskQueueManager::GetNextSequenceNumber() {
   return task_sequence_num_.GetNext();
 }
 
+int TaskQueueManager::GetNextAgeNumber() {
+  return task_age_num_.GetNext();
+}
+
 scoped_refptr<base::trace_event::ConvertableToTraceFormat>
 TaskQueueManager::AsValueWithSelectorResult(
     bool should_run,
     internal::TaskQueueImpl* selected_queue) const {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   scoped_refptr<base::trace_event::TracedValue> state =
       new base::trace_event::TracedValue();
   state->BeginArray("queues");
   for (auto& queue : queues_)
     queue->AsValueInto(state.get());
@@ skipping 10 matching lines @@
   state->EndArray();
   return state;
 }
 
 void TaskQueueManager::OnTaskQueueEnabled() {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   MaybePostDoWorkOnMainRunner();
 }
 
 }  // namespace scheduler