TaskScheduler: Pop a Task from its Sequence from SchedulerWorkerThread.

base/task_scheduler/scheduler_worker_thread.cc

Index: base/task_scheduler/scheduler_worker_thread.cc
diff --git a/base/task_scheduler/scheduler_worker_thread.cc b/base/task_scheduler/scheduler_worker_thread.cc
index 49dde51d6a7b036675fd47d645df60e0c0e4e242..ec2b289ec933c1271ed52d8ad2ed566142be3904 100644
--- a/base/task_scheduler/scheduler_worker_thread.cc
+++ b/base/task_scheduler/scheduler_worker_thread.cc
@@ -74,7 +74,10 @@ void SchedulerWorkerThread::ThreadMain() {
     }
 
     task_tracker_->RunTask(sequence->PeekTask());
-    delegate_->RanTaskFromSequence(std::move(sequence));
+
+    const bool sequence_became_empty = sequence->PopTask();

[gab, 2016/04/07 21:37:33]

In other places you have comments explaining why this atomic operation always
leads to the correct state (i.e. either we made it atomically empty and the next
Add() will be in charge of re-inserting or there was a task behind our pop and
we're in charge of re-inserting).
Think it's worth re-iterating the algorithmic guarantees relied on here?

[fdoray, 2016/04/08 15:59:12]

Done.

+    if (!sequence_became_empty)
+      delegate_->EnqueueSequence(std::move(sequence));
 
     // Calling WakeUp() guarantees that this SchedulerWorkerThread will run
     // Tasks from Sequences returned by the GetWork() method of |delegate_|