Make PendingTask move-only and pass it by value on retaining params

base/message_loop/incoming_task_queue.cc

Index: base/message_loop/incoming_task_queue.cc
diff --git a/base/message_loop/incoming_task_queue.cc b/base/message_loop/incoming_task_queue.cc
index 05bb28891c9b922f2d81e6494c77ba934372a101..d40d5d5dddaed597da72a992fb6ca5de8f06a249 100644
--- a/base/message_loop/incoming_task_queue.cc
+++ b/base/message_loop/incoming_task_queue.cc
@@ -155,8 +155,8 @@ bool IncomingTaskQueue::PostPendingTask(PendingTask* pending_task) {
                                                 *pending_task);
 
   bool was_empty = incoming_queue_.empty();
-  incoming_queue_.push(*pending_task);
-  pending_task->task.Reset();
+  incoming_queue_.push(std::move(*pending_task));
+  DCHECK(pending_task->task.is_null());

[Sami, 2016/04/13 11:33:00]

Is this a valid assumption? I thought we should treat the moved-from object as
undefined after the move.

[tzik, 2016/04/13 14:35:37]

Done.

[Sami, 2016/04/13 15:17:32]

I'm not sure we need to even do this. We've moved pending_task to the incoming
queue so it's no longer our concern :)

[tzik, 2016/04/14 19:44:30]

Right, it's redundant since we know the move construction on Callback clears the
object. I added it just for readability and for making sure, since it's legal to
leave something non-null there as WTF containers do.

 
   if (is_ready_for_scheduling_ &&
       (always_schedule_work_ || (!message_loop_scheduled_ && was_empty))) {