Flush TaskScheduler in ~ScopedTaskEnvironment and ~ScopedAsyncTaskScheduler.

base/test/scoped_task_environment.cc

Index: base/test/scoped_task_environment.cc
diff --git a/base/test/scoped_task_environment.cc b/base/test/scoped_task_environment.cc
index 8744b4a6b11427fe84c82bb7567708fff11b552c..b18bf6a19d3a940ba0268f1dcb4409780d108cf5 100644
--- a/base/test/scoped_task_environment.cc
+++ b/base/test/scoped_task_environment.cc
@@ -32,6 +32,9 @@ ScopedTaskEnvironment::~ScopedTaskEnvironment() {
   RunLoop().RunUntilIdle();
 
   DCHECK_EQ(TaskScheduler::GetInstance(), task_scheduler_);
+  // Without FlushForTesting(), DeleteSoon() and ReleaseSoon() tasks could be
+  // skipped, resulting in memory leaks.
+  TaskScheduler::GetInstance()->FlushForTesting();
   TaskScheduler::GetInstance()->Shutdown();
   TaskScheduler::GetInstance()->JoinForTesting();
   TaskScheduler::SetInstance(nullptr);