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..7e6a1eb4f314c61d2bee23eb9c2db117d8d0e386 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"
 
@@ -17,19 +18,19 @@ namespace media {
 class DataSource;
 
 // An implementation of FFmpegURLProtocol that blocks until the underlying
-// asynchronous DataSource::Read() operation completes.
+// asynchronous DataSource::Read() operation completes. Generally constructed on
+// the media thread and used by ffmpeg through the AVIO interface from a
+// sequenced blocking pool.
 class MEDIA_EXPORT BlockingUrlProtocol : public FFmpegURLProtocol {
  public:
   // Implements FFmpegURLProtocol using the given |data_source|. |error_cb| is
   // fired any time DataSource::Read() returns an error.
-  //
-  // TODO(scherkus): After all blocking operations are isolated on a separate
-  // thread we should be able to eliminate |error_cb|.
   BlockingUrlProtocol(DataSource* data_source, const base::Closure& error_cb);
   virtual ~BlockingUrlProtocol();
 
   // Aborts any pending reads by returning a read error. After this method
-  // returns all subsequent calls to Read() will immediately fail.
+  // returns all subsequent calls to Read() will immediately fail. May be called
+  // from any thread and upon return ensures no further use of |data_source_|.
   void Abort();
 
   // FFmpegURLProtocol implementation.
@@ -44,8 +45,14 @@ class MEDIA_EXPORT BlockingUrlProtocol : public FFmpegURLProtocol {
   // has completed.
   void SignalReadCompleted(int size);
 
+  // |data_source_lock_| allows Abort() to be called from any thread and stop
+  // all outstanding access to |data_source_|. Typically Abort() is called from
+  // the media thread while ffmpeg is operating on another thread.
+  base::Lock data_source_lock_;
   DataSource* data_source_;
+
   base::Closure error_cb_;
+  const bool is_streaming_;
 
   // Used to unblock the thread during shutdown and when reads complete.
   base::WaitableEvent aborted_;