Speculative patch: Make it safe to delete the TQM inside a Task

content/child/scheduler/task_queue_manager.h

 // 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.
 
 #ifndef CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_MANAGER_H_
 #define CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_MANAGER_H_
 
 #include "base/atomic_sequence_num.h"
 #include "base/debug/task_annotator.h"
 #include "base/macros.h"
@@ skipping 110 matching lines @@
   // manager executes its tasks on.
   void AddTaskObserver(base::MessageLoop::TaskObserver* task_observer);
   void RemoveTaskObserver(base::MessageLoop::TaskObserver* task_observer);
 
   void SetTimeSourceForTesting(scoped_refptr<cc::TestNowSource> time_source);
 
  private:
   friend class internal::LazyNow;
   friend class internal::TaskQueue;
 
+  class DeletionSentinel : public base::RefCounted<DeletionSentinel> {
+   private:
+    friend class base::RefCounted<DeletionSentinel>;
+    ~DeletionSentinel() {}
+  };
+
   // Called by the task queue to register a new pending task and allocate a
   // sequence number for it.
   void DidQueueTask(base::PendingTask* pending_task);
 
   // Post a task to call DoWork() on the main task runner.  Only one pending
   // DoWork is allowed from the main thread, to prevent an explosion of pending
   // DoWorks.
   void MaybePostDoWorkOnMainRunner();
 
   // Use the selector to choose a pending task and run it.
@@ skipping 50 matching lines @@
   int pending_dowork_count_;
 
   int work_batch_size_;
 
   scoped_refptr<cc::TestNowSource> time_source_;
 
   ObserverList<base::MessageLoop::TaskObserver> task_observers_;
 
   const char* disabled_by_default_tracing_category_;
 
+  scoped_refptr<DeletionSentinel> deletion_sentinel_;
   base::WeakPtrFactory<TaskQueueManager> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(TaskQueueManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_MANAGER_H_