Run ScopedTaskScheduler tasks synchronously.

base/task_scheduler/task_tracker.cc

Index: base/task_scheduler/task_tracker.cc
diff --git a/base/task_scheduler/task_tracker.cc b/base/task_scheduler/task_tracker.cc
index 4c1ee8da3dd285ea1f668cab15b4f4565e91059e..e28148b96221e8a5ddc7fda27234cf7726d33f5b 100644
--- a/base/task_scheduler/task_tracker.cc
+++ b/base/task_scheduler/task_tracker.cc
@@ -288,6 +288,14 @@ bool TaskTracker::IsShutdownComplete() const {
 }
 
 void TaskTracker::SetHasShutdownStartedForTesting() {
+  AutoSchedulerLock auto_lock(shutdown_lock_);
+
+  // Create |shutdown_event_| to avoid a DCHECK failure when a task blocking

[gab, 2016/12/08 20:15:45]

// Create a dummy |shutdown_event_| to satisfy TaskTracker's expectation of its
existence during shutdown (e.g. in OnBlockingShutdownTasksComplete()).

[fdoray, 2016/12/09 16:26:41]

Done.

+  // shutdown completes its execution.
+  shutdown_event_.reset(
+      new WaitableEvent(WaitableEvent::ResetPolicy::MANUAL,
+                        WaitableEvent::InitialState::NOT_SIGNALED));
+
   state_->StartShutdown();
 }