Replace base::Callback with base::OnceCallback in base::PendingTask

base/task_scheduler/sequence.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_H_
 #define BASE_TASK_SCHEDULER_SEQUENCE_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 27 matching lines @@
 //
 // This class is thread-safe.
 class BASE_EXPORT Sequence : public RefCountedThreadSafe<Sequence> {
  public:
   Sequence();
 
   // Adds |task| at the end of the sequence's queue. Returns true if the
   // sequence was empty before this operation.
   bool PushTask(std::unique_ptr<Task> task);
 
   // Returns the task in front of the sequence's queue, if any.

[fdoray, 2016/10/06 17:37:22]

// The returned Task is non-const to allow running its OnceClosure. Any other
mutation may result in undefined behavior.

[tzik, 2016/10/13 05:58:04]

Reverted this part per your CL.

-  const Task* PeekTask() const;
+  Task* PeekTask() const;
 
   // Removes the task in front of the sequence's queue. Returns true if the
   // sequence is empty after this operation. Cannot be called on an empty
   // sequence.
   bool PopTask();
 
   // Returns a SequenceSortKey representing the priority of the sequence. Cannot
   // be called on an empty sequence.
   SequenceSortKey GetSortKey() const;
 
@@ skipping 16 matching lines @@
   size_t num_tasks_per_priority_[static_cast<int>(TaskPriority::HIGHEST) + 1] =
       {};
 
   DISALLOW_COPY_AND_ASSIGN(Sequence);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_SEQUENCE_H_