TaskScheduler: Avoid Sequence refcount bump in GetWork()

base/task_scheduler/sequence_sort_key.h

 // Copyright 2016 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.
 
 #ifndef BASE_TASK_SCHEDULER_SEQUENCE_SORT_KEY_H_
 #define BASE_TASK_SCHEDULER_SEQUENCE_SORT_KEY_H_
 
 #include "base/base_export.h"
 #include "base/task_scheduler/task_traits.h"
 #include "base/time/time.h"
 
 namespace base {
 namespace internal {
 
 // An immutable representation of the priority of a Sequence.

[danakj, 2016/04/27 20:50:59]

maybe you should say "immutable but copyable" or "immutable but assignable"

[gab, 2016/04/28 13:47:15]

Done.

-struct BASE_EXPORT SequenceSortKey final {
+class BASE_EXPORT SequenceSortKey final {
+ public:
   SequenceSortKey(TaskPriority priority, TimeTicks next_task_sequenced_time);
 
   bool operator<(const SequenceSortKey& other) const;
   bool operator>(const SequenceSortKey& other) const { return other < *this; }
 
+  bool operator==(const SequenceSortKey& other) const {
+    return priority_ == other.priority_ &&
+           next_task_sequenced_time_ == other.next_task_sequenced_time_;
+  }
+  bool operator!=(const SequenceSortKey& other) const {
+    return !(other == *this);
+  };
+
+ private:
+  // The private section allows this class to keep its immutable property while
+  // being copy-assignable (i.e. instead of making its members const).
+
   // Highest task priority in the sequence at the time this sort key was
   // created.
-  const TaskPriority priority;
+  TaskPriority priority_;
 
   // Sequenced time of the next task to run in the sequence at the time this
   // sort key was created.
-  const TimeTicks next_task_sequenced_time;
+  TimeTicks next_task_sequenced_time_;
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_SEQUENCE_SORT_KEY_H_