Revert of Replace FFmpegDemuxer thread per element with base::TaskScheduler.

media/test/pipeline_integration_test_base.cc

Index: media/test/pipeline_integration_test_base.cc
diff --git a/media/test/pipeline_integration_test_base.cc b/media/test/pipeline_integration_test_base.cc
index 3902b1f21b56f1c388c1f164752e2d4e9db36f0b..6115e472de8fe8c4af21db49b25b12d4e5cced96 100644
--- a/media/test/pipeline_integration_test_base.cc
+++ b/media/test/pipeline_integration_test_base.cc
@@ -59,7 +59,6 @@
   if (pipeline_->IsRunning())
     Stop();
 
-  demuxer_.reset();
   pipeline_.reset();
   base::RunLoop().RunUntilIdle();
 }
@@ -311,7 +310,6 @@
   data_source_ = std::move(data_source);
 
 #if !defined(MEDIA_DISABLE_FFMPEG)
-  task_scheduler_.reset(new base::test::ScopedTaskScheduler(&message_loop_));
   demuxer_ = std::unique_ptr<Demuxer>(new FFmpegDemuxer(
       message_loop_.task_runner(), data_source_.get(),
       base::Bind(&PipelineIntegrationTestBase::DemuxerEncryptedMediaInitDataCB,