Run ScopedTaskScheduler tasks synchronously.

base/task_scheduler/task_tracker.cc

 // Copyright 2016 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 "base/task_scheduler/task_tracker.h"
 
 #include <limits>
 
 #include "base/callback.h"
 #include "base/debug/task_annotator.h"
@@ skipping 270 matching lines @@
 bool TaskTracker::HasShutdownStarted() const {
   return state_->HasShutdownStarted();
 }
 
 bool TaskTracker::IsShutdownComplete() const {
   AutoSchedulerLock auto_lock(shutdown_lock_);
   return shutdown_event_ && shutdown_event_->IsSignaled();
 }
 
 void TaskTracker::SetHasShutdownStartedForTesting() {
+  AutoSchedulerLock auto_lock(shutdown_lock_);
+
+  // Create a dummy |shutdown_event_| to satisfy TaskTracker's expectation of
+  // its existence during shutdown (e.g. in OnBlockingShutdownTasksComplete()).
+  shutdown_event_.reset(
+      new WaitableEvent(WaitableEvent::ResetPolicy::MANUAL,
+                        WaitableEvent::InitialState::NOT_SIGNALED));
+
   state_->StartShutdown();
 }
 
 void TaskTracker::PerformRunTask(std::unique_ptr<Task> task) {
   debug::TaskAnnotator().RunTask(kQueueFunctionName, task.get());
 }
 
 void TaskTracker::PerformShutdown() {
   {
     AutoSchedulerLock auto_lock(shutdown_lock_);
@@ skipping 149 matching lines @@
       subtle::NoBarrier_AtomicIncrement(&num_pending_undelayed_tasks_, -1);
   DCHECK_GE(new_num_pending_undelayed_tasks, 0);
   if (new_num_pending_undelayed_tasks == 0) {
     AutoSchedulerLock auto_lock(flush_lock_);
     flush_cv_->Signal();
   }
 }
 
 }  // namespace internal
 }  // namespace base