RundownTaskCounter needs to use a non-nestable task to block on the completion of already scheduled…

chrome/browser/browser_process_impl.cc

 // 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.
 
 #include "chrome/browser/browser_process_impl.h"
 
 #include <algorithm>
 #include <map>
 #include <vector>
 
@@ skipping 408 matching lines @@
     : count_(1), waitable_event_(true, false) {
 }
 
 void RundownTaskCounter::Post(base::SequencedTaskRunner* task_runner) {
   // As the count starts off at one, it should never get to zero unless
   // TimedWait has been called.
   DCHECK(!base::AtomicRefCountIsZero(&count_));
 
   base::AtomicRefCountInc(&count_);
 
-  task_runner->PostTask(FROM_HERE,
+  // The task must be non-nestable to guarantee that it runs after all tasks
+  // currently scheduled on |task_runner| have completed.
+  task_runner->PostNonNestableTask(FROM_HERE,
       base::Bind(&RundownTaskCounter::Decrement, this));
 }
 
 void RundownTaskCounter::Decrement() {
   if (!base::AtomicRefCountDec(&count_))
     waitable_event_.Signal();
 }
 
 bool RundownTaskCounter::TimedWait(const base::TimeDelta& max_time) {
   // Decrement the excess count from the constructor.
@@ skipping 761 matching lines @@
 }
 
 void BrowserProcessImpl::OnAutoupdateTimer() {
   if (CanAutorestartForUpdate()) {
     DLOG(WARNING) << "Detected update.  Restarting browser.";
     RestartBackgroundInstance();
   }
 }
 
 #endif  // (defined(OS_WIN) || defined(OS_LINUX)) && !defined(OS_CHROMEOS)