scheduler: Maintain a constant enqueue order for every task

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

Index: third_party/WebKit/Source/platform/scheduler/base/enqueue_order.cc
diff --git a/third_party/WebKit/Source/platform/scheduler/base/enqueue_order.cc b/third_party/WebKit/Source/platform/scheduler/base/enqueue_order.cc
index fcfd3ffdd817f4160af9c23e4f65752af447d972..d5fc4f9e2755a0c02d411a6a1ad48508e259ac79 100644
--- a/third_party/WebKit/Source/platform/scheduler/base/enqueue_order.cc
+++ b/third_party/WebKit/Source/platform/scheduler/base/enqueue_order.cc
@@ -8,16 +8,48 @@ 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<SequenceNumber>(
+          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_++};
+}
+
+EnqueueOrder::EnqueueOrder() : sequence_num(0) {}
+
+EnqueueOrder::EnqueueOrder(base::TimeTicks delayed_run_time,
+                           SequenceNumber sequence_num)
+    : delayed_run_time(delayed_run_time), sequence_num(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