scheduler: Maintain a constant enqueue order for every task

third_party/WebKit/Source/platform/scheduler/base/task_queue_impl.h

Index: third_party/WebKit/Source/platform/scheduler/base/task_queue_impl.h
diff --git a/third_party/WebKit/Source/platform/scheduler/base/task_queue_impl.h b/third_party/WebKit/Source/platform/scheduler/base/task_queue_impl.h
index 02be214e55591f00dd7fc00dd2c297678b504743..4fd195ff28b37cab3069b8f5e39d383aad2675c9 100644
--- a/third_party/WebKit/Source/platform/scheduler/base/task_queue_impl.h
+++ b/third_party/WebKit/Source/platform/scheduler/base/task_queue_impl.h
@@ -49,8 +49,7 @@ class WorkQueueSets;
 // Delayed tasks are initially posted to delayed_incoming_queue and a wake-up
 // is scheduled with the TimeDomain.  When the delay has elapsed, the TimeDomain
 // calls UpdateDelayedWorkQueue and ready delayed tasks are moved into the
-// delayed_work_queue.  Note the EnqueueOrder (used for ordering) for a delayed
-// task is not set until it's moved into the delayed_work_queue.
+// delayed_work_queue.
 //
 // TaskQueueImpl uses the WorkQueueSets and the TaskQueueSelector to implement
 // prioritization. Task selection is done by the TaskQueueSelector and when a
@@ -85,8 +84,7 @@ class BLINK_PLATFORM_EXPORT TaskQueueImpl final : public TaskQueue {
     Task();
     Task(const tracked_objects::Location& posted_from,
          base::OnceClosure task,
-         base::TimeTicks desired_run_time,
-         EnqueueOrder sequence_number,
+         EnqueueOrder enqueue_order,
          bool nestable);
 
     Task(const tracked_objects::Location& posted_from,
@@ -101,28 +99,10 @@ class BLINK_PLATFORM_EXPORT TaskQueueImpl final : public TaskQueue {
     }
 
     EnqueueOrder enqueue_order() const {
-#ifndef NDEBUG
-      DCHECK(enqueue_order_set_);
-#endif
       return enqueue_order_;
     }
 
-    void set_enqueue_order(EnqueueOrder enqueue_order) {
-#ifndef NDEBUG
-      DCHECK(!enqueue_order_set_);
-      enqueue_order_set_ = true;
-#endif
-      enqueue_order_ = enqueue_order;
-    }
-
-#ifndef NDEBUG
-    bool enqueue_order_set() const { return enqueue_order_set_; }
-#endif
-
    private:
-#ifndef NDEBUG
-    bool enqueue_order_set_;
-#endif
     // Similar to sequence number, but ultimately the |enqueue_order_| is what
     // the scheduler uses for task ordering. For immediate tasks |enqueue_order|
     // is set when posted, but for delayed tasks it's not defined until they are
@@ -219,7 +199,7 @@ class BLINK_PLATFORM_EXPORT TaskQueueImpl final : public TaskQueue {
   }
 
   void PushImmediateIncomingTaskForTest(TaskQueueImpl::Task&& task);
-  EnqueueOrder GetFenceForTest() const;
+  uint64_t GetFenceForTest() const;
 
   class QueueEnabledVoterImpl : public QueueEnabledVoter {
    public:
@@ -284,7 +264,7 @@ class BLINK_PLATFORM_EXPORT TaskQueueImpl final : public TaskQueue {
     int is_enabled_refcount;
     int voter_refcount;
     base::trace_event::BlameContext* blame_context;  // Not owned.
-    EnqueueOrder current_fence;
+    uint64_t current_fence;
     base::TimeTicks scheduled_time_domain_wake_up;
   };
 
@@ -317,8 +297,7 @@ class BLINK_PLATFORM_EXPORT TaskQueueImpl final : public TaskQueue {
   void PushOntoImmediateIncomingQueueLocked(
       const tracked_objects::Location& posted_from,
       base::OnceClosure task,
-      base::TimeTicks desired_run_time,
-      EnqueueOrder sequence_number,
+      EnqueueOrder enqueue_order,
       bool nestable);
 
   // Extracts all the tasks from the immediate incoming queue and clears it.