[scheduler]: Fix a bug with non-nestable tasks.

components/scheduler/child/task_queue_manager.cc

 // Copyright 2014 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.
 
 #include "components/scheduler/child/task_queue_manager.h"
 
 #include <queue>
 #include <set>
 
 #include "base/bind.h"
@@ skipping 283 matching lines @@
 
     // Detect if the TaskQueueManager just got deleted.  If this happens we must
     // not access any member variables after this point.
     if (protect->HasOneRef())
       return true;
 
     if (queue->GetShouldNotifyObservers()) {
       FOR_EACH_OBSERVER(base::MessageLoop::TaskObserver, task_observers_,
                         DidProcessTask(pending_task));
     }
+  }
 
-    pending_task.task.Reset();
-    *out_previous_task = pending_task;
-  }
+  pending_task.task.Reset();
+  *out_previous_task = pending_task;

[Sami, 2015/08/12 11:47:51]

Hmm, should we just ignore out_previous_task if we decided to actually not run
it? It feels wrong if a non-nestable task will still cause a wakeup even though
we didn't actually run it. WDYT?

I guess one way would be to have this function return a tri-state enum to say
what it actually did.

[rmcilroy, 2015/08/12 13:08:27]

As discussed offline, this might be our only chance to wake up an after wakeup
queue because we will never get notified when the non-nestable task gets run.
Add a comment as discussed.

   return false;
 }
 
 bool TaskQueueManager::RunsTasksOnCurrentThread() const {
   return main_task_runner_->RunsTasksOnCurrentThread();
 }
 
 bool TaskQueueManager::PostDelayedTask(
     const tracked_objects::Location& from_here,
     const base::Closure& task,
@@ skipping 65 matching lines @@
 }
 
 void TaskQueueManager::OnTaskQueueEnabled(internal::TaskQueueImpl* queue) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   // Only schedule DoWork if there's something to do.
   if (!queue->work_queue().empty())
     MaybePostDoWorkOnMainRunner();
 }
 
 }  // namespace scheduler