Trace PostTasks from post to run

base/message_loop.h

 // Copyright (c) 2012 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 BASE_MESSAGE_LOOP_H_
 #define BASE_MESSAGE_LOOP_H_
 
 #include <queue>
 #include <string>
 
@@ skipping 487 matching lines @@
 
   base::RunLoop* run_loop_;
 
 #if defined(OS_WIN)
   base::TimeTicks high_resolution_timer_expiration_;
   // Should be set to true before calling Windows APIs like TrackPopupMenu, etc
   // which enter a modal message loop.
   bool os_modal_loop_;
 #endif
 
-  // The next sequence number to use for delayed tasks.
+  // The next sequence number to use for delayed tasks. Updating this counter is
+  // protected by incoming_queue_lock_.
   int next_sequence_num_;
 
   ObserverList<TaskObserver> task_observers_;
 
   // The message loop proxy associated with this message loop, if one exists.
   scoped_refptr<base::MessageLoopProxy> message_loop_proxy_;
   scoped_ptr<base::ThreadTaskRunnerHandle> thread_task_runner_handle_;
 
  private:
   template <class T, class R> friend class base::subtle::DeleteHelperInternal;
@@ skipping 152 matching lines @@
 #endif  // defined(OS_POSIX)
 };
 
 // Do not add any member variables to MessageLoopForIO!  This is important b/c
 // MessageLoopForIO is often allocated via MessageLoop(TYPE_IO).  Any extra
 // data that you need should be stored on the MessageLoop's pump_ instance.
 COMPILE_ASSERT(sizeof(MessageLoop) == sizeof(MessageLoopForIO),
                MessageLoopForIO_should_not_have_extra_member_variables);
 
 #endif  // BASE_MESSAGE_LOOP_H_