TaskScheduler: Always remove SchedulerWorker from idle stack on wake up.

base/task_scheduler/scheduler_worker_pool_impl.h

Index: base/task_scheduler/scheduler_worker_pool_impl.h
diff --git a/base/task_scheduler/scheduler_worker_pool_impl.h b/base/task_scheduler/scheduler_worker_pool_impl.h
index a621f797a53473b2096170a07689e456d5c3f2de..b5aa894e38afdaafce3c2933d46d4bf97ab7a6e3 100644
--- a/base/task_scheduler/scheduler_worker_pool_impl.h
+++ b/base/task_scheduler/scheduler_worker_pool_impl.h
@@ -114,6 +114,9 @@ class BASE_EXPORT SchedulerWorkerPoolImpl : public SchedulerWorkerPool {
       size_t max_threads,
       const ReEnqueueSequenceCallback& re_enqueue_sequence_callback);
 
+  // Wakes up |worker|.
+  void WakeUpWorker(SchedulerWorker* worker);
+
   // Wakes up the last worker from this worker pool to go idle, if any.
   void WakeUpOneWorker();
 
@@ -159,7 +162,11 @@ class BASE_EXPORT SchedulerWorkerPoolImpl : public SchedulerWorkerPool {
   // details in GetWork()).
   mutable SchedulerLock idle_workers_stack_lock_;
 
-  // Stack of idle workers.
+  // Stack of idle workers. Initially, all workers are on this stack. A worker
+  // is removed from the stack before its WakeUp() function is called and when
+  // it receives work from GetWork() (a worker calls GetWork() when its sleep
+  // timeout expires, even if its WakeUp() method hasn't been called). A worker
+  // is pushed on this stack when it receives nullptr from GetWork().
   SchedulerWorkerStack idle_workers_stack_;
 
   // Signaled when all workers become idle.