Replace FFmpegDemuxer thread per element with base::TaskScheduler.

media/filters/blocking_url_protocol.h

Index: media/filters/blocking_url_protocol.h
diff --git a/media/filters/blocking_url_protocol.h b/media/filters/blocking_url_protocol.h
index 4f9ef4f3507490cf957186a8c937db5da498d42f..892b1d501ecaf7ecc85ed21bcc58728cbd316113 100644
--- a/media/filters/blocking_url_protocol.h
+++ b/media/filters/blocking_url_protocol.h
@@ -9,6 +9,7 @@
 
 #include "base/callback.h"
 #include "base/macros.h"
+#include "base/synchronization/lock.h"
 #include "base/synchronization/waitable_event.h"
 #include "media/filters/ffmpeg_glue.h"
 
@@ -44,8 +45,10 @@ class MEDIA_EXPORT BlockingUrlProtocol : public FFmpegURLProtocol {
   // has completed.
   void SignalReadCompleted(int size);
 
+  base::Lock data_source_lock_;

[xhwang, 2017/02/23 23:45:42]

Can you provide a comment why we need this lock, e.g. |data_source_| can be
access on which threads.

[DaleCurtis, 2017/02/24 23:40:29]

Done.

   DataSource* data_source_;

[xhwang, 2017/02/23 23:45:42]

nit: add an empty line here so that it's more clear that the lock only protects
|data_source_|

[DaleCurtis, 2017/02/24 23:40:29]

Done.

   base::Closure error_cb_;
+  const bool is_streaming_;
 
   // Used to unblock the thread during shutdown and when reads complete.
   base::WaitableEvent aborted_;