Flush TaskScheduler in ~ScopedTaskEnvironment and ~ScopedAsyncTaskScheduler.

base/test/scoped_async_task_scheduler.cc

Index: base/test/scoped_async_task_scheduler.cc
diff --git a/base/test/scoped_async_task_scheduler.cc b/base/test/scoped_async_task_scheduler.cc
index 397243edb0588fa90778ee927e64f36f6ef3d25e..a2cfca0c20c99d8ae234a1ab9b77085ee2e59c31 100644
--- a/base/test/scoped_async_task_scheduler.cc
+++ b/base/test/scoped_async_task_scheduler.cc
@@ -29,6 +29,7 @@ ScopedAsyncTaskScheduler::ScopedAsyncTaskScheduler() {
 
 ScopedAsyncTaskScheduler::~ScopedAsyncTaskScheduler() {
   DCHECK_EQ(TaskScheduler::GetInstance(), task_scheduler_);
+  TaskScheduler::GetInstance()->FlushForTesting();
   TaskScheduler::GetInstance()->Shutdown();
   TaskScheduler::GetInstance()->JoinForTesting();
   TaskScheduler::SetInstance(nullptr);