Replace FFmpegDemuxer thread per element with base::TaskScheduler.

media/test/pipeline_integration_test_base.h

Index: media/test/pipeline_integration_test_base.h
diff --git a/media/test/pipeline_integration_test_base.h b/media/test/pipeline_integration_test_base.h
index 192d6f837220cf5b1af795ced11046934d4383e0..580e963c658f7b0261a6b2e6c7e2b392a352a88f 100644
--- a/media/test/pipeline_integration_test_base.h
+++ b/media/test/pipeline_integration_test_base.h
@@ -11,6 +11,7 @@
 #include "base/md5.h"
 #include "base/memory/scoped_vector.h"
 #include "base/message_loop/message_loop.h"
+#include "base/test/scoped_task_scheduler.h"
 #include "media/audio/clockless_audio_sink.h"
 #include "media/audio/null_audio_sink.h"
 #include "media/base/demuxer.h"
@@ -133,6 +134,9 @@ class PipelineIntegrationTestBase : public Pipeline::Client {
   base::MD5Context md5_context_;
   bool hashing_enabled_;
   bool clockless_playback_;
+
+  // TaskScheduler is used only for FFmpegDemuxer.
+  std::unique_ptr<base::test::ScopedTaskScheduler> task_scheduler_;
   std::unique_ptr<Demuxer> demuxer_;
   std::unique_ptr<DataSource> data_source_;
   std::unique_ptr<PipelineImpl> pipeline_;