scheduler: Maintain a constant enqueue order for every task

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

 // Copyright 2015 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 "platform/scheduler/base/enqueue_order.h"
 
 namespace blink {
 namespace scheduler {
 namespace internal {
 
-// Note we set the first |enqueue_order_| to a specific non-zero value, because
+// Note we set the first sequence number to a specific non-zero value, because
 // first N values of EnqueueOrder have special meaning (see EnqueueOrderValues).
 EnqueueOrderGenerator::EnqueueOrderGenerator()
-    : enqueue_order_(static_cast<EnqueueOrder>(EnqueueOrderValues::FIRST)) {}
+    : sequence_num_(
+          static_cast<uint64_t>(EnqueueOrderSequenceNumberValues::FIRST)) {}
 
 EnqueueOrderGenerator::~EnqueueOrderGenerator() {}
 
-EnqueueOrder EnqueueOrderGenerator::GenerateNext() {
+EnqueueOrder EnqueueOrderGenerator::GenerateNext(
+    base::TimeTicks delayed_run_time) {
   base::AutoLock lock(lock_);
-  return enqueue_order_++;
+  return {delayed_run_time, sequence_num_++};
+}
+
+bool EnqueueOrder::operator==(const EnqueueOrder& other) const {
+  return delayed_run_time == other.delayed_run_time &&
+         sequence_num == other.sequence_num;
+}
+
+bool EnqueueOrder::operator<=(const EnqueueOrder& other) const {
+  if (delayed_run_time > other.delayed_run_time)
+    return false;
+
+  if (delayed_run_time < other.delayed_run_time)
+    return true;
+
+  return sequence_num <= other.sequence_num;
+}
+
+bool EnqueueOrder::operator<(const EnqueueOrder& other) const {
+  return !(*this == other) && *this <= other;
+}
+
+std::ostream& operator<<(std::ostream& stream, const EnqueueOrder& value) {
+  return stream << "(" << value.delayed_run_time << ", " << value.sequence_num
+                << ")";
 }
 
 }  // namespace internal
 }  // namespace scheduler
 }  // namespace blink