Revert of Explicitly track the scheduler task enqueueing order in a new field

components/scheduler/child/task_queue_manager.cc

Index: components/scheduler/child/task_queue_manager.cc
diff --git a/components/scheduler/child/task_queue_manager.cc b/components/scheduler/child/task_queue_manager.cc
index 5906f7a68e21ffb797f190de1b77bb76748bd639..c557665ab7a4b6a5fac49b02fa6f58a461135f56 100644
--- a/components/scheduler/child/task_queue_manager.cc
+++ b/components/scheduler/child/task_queue_manager.cc
@@ -104,7 +104,7 @@
 
 void TaskQueueManager::UpdateWorkQueues(
     bool should_trigger_wakeup,
-    const internal::TaskQueueImpl::Task* previous_task) {
+    const base::PendingTask* previous_task) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   internal::LazyNow lazy_now(this);
 
@@ -125,6 +125,11 @@
     // as the iterator isn't the element being delated.
     if (queue->work_queue().empty())
         queue->UpdateWorkQueue(&lazy_now, should_trigger_wakeup, previous_task);
+    if (!queue->work_queue().empty()) {
+      // Currently we should not be getting tasks with delayed run times in any
+      // of the work queues.
+      DCHECK(queue->work_queue().front().delayed_run_time.is_null());
+    }
   }
 }
 
@@ -154,7 +159,8 @@
   // pump-after-wakeup queue.
   UpdateWorkQueues(false, nullptr);
 
-  internal::TaskQueueImpl::Task previous_task;
+  base::PendingTask previous_task((tracked_objects::Location()),
+                                  (base::Closure()));
   for (int i = 0; i < work_batch_size_; i++) {
     internal::TaskQueueImpl* queue;
     if (!SelectQueueToService(&queue))
@@ -186,18 +192,16 @@
   return should_run;
 }
 
-void TaskQueueManager::DidQueueTask(
-    const internal::TaskQueueImpl::Task& pending_task) {
+void TaskQueueManager::DidQueueTask(const base::PendingTask& pending_task) {
   task_annotator_.DidQueueTask("TaskQueueManager::PostTask", pending_task);
 }
 
 bool TaskQueueManager::ProcessTaskFromWorkQueue(
     internal::TaskQueueImpl* queue,
-    internal::TaskQueueImpl::Task* out_previous_task) {
+    base::PendingTask* out_previous_task) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   scoped_refptr<DeletionSentinel> protect(deletion_sentinel_);
-  // TODO(alexclarke): consider std::move() when allowed.
-  internal::TaskQueueImpl::Task pending_task = queue->TakeTaskFromWorkQueue();
+  base::PendingTask pending_task = queue->TakeTaskFromWorkQueue();
 
   if (queue->GetQuiescenceMonitored())
     task_was_run_on_quiescence_monitored_queue_ = true;