scheduler: Maintain a constant enqueue order for every task

third_party/WebKit/Source/platform/scheduler/base/task_queue_selector.cc

Index: third_party/WebKit/Source/platform/scheduler/base/task_queue_selector.cc
diff --git a/third_party/WebKit/Source/platform/scheduler/base/task_queue_selector.cc b/third_party/WebKit/Source/platform/scheduler/base/task_queue_selector.cc
index 0a24636c20c8082417c45cf28ef6cf86e92ab559..abddb683d3b47015ebdf67e6bab154bc6cbb1fce 100644
--- a/third_party/WebKit/Source/platform/scheduler/base/task_queue_selector.cc
+++ b/third_party/WebKit/Source/platform/scheduler/base/task_queue_selector.cc
@@ -170,7 +170,12 @@ bool TaskQueueSelector::PrioritizingSelector::
     EnqueueOrder delayed_enqueue_order;
     if (delayed_work_queue_sets_.GetOldestQueueAndEnqueueOrderInSet(
             priority, &delayed_queue, &delayed_enqueue_order)) {
-      if (immediate_enqueue_order < delayed_enqueue_order) {
+      // When comparing enqueue orders of immediate and delayed tasks, only look
+      // at the sequence number because the delay has already been applied. Note
+      // that the delayed run time is still taken into account by TaskQueueSets
+      // when comparing tasks across different queues.
+      if (immediate_enqueue_order.sequence_num <
+          delayed_enqueue_order.sequence_num) {
         *out_work_queue = immediate_queue;
       } else {
         *out_chose_delayed_over_immediate = true;