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

base/task_scheduler/sequence.h

Index: base/task_scheduler/sequence.h
diff --git a/base/task_scheduler/sequence.h b/base/task_scheduler/sequence.h
index 8717336080e623dfde5ce8e5acc108ebcc9e61c0..bace70be1f5063f103acd507ad47299cd105ccb0 100644
--- a/base/task_scheduler/sequence.h
+++ b/base/task_scheduler/sequence.h
@@ -46,7 +46,7 @@ class BASE_EXPORT Sequence : public RefCountedThreadSafe<Sequence> {
   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