Fix race when calling GetWeakPtr() from multiple threads.

media/blink/buffered_data_source.h

Index: media/blink/buffered_data_source.h
diff --git a/media/blink/buffered_data_source.h b/media/blink/buffered_data_source.h
index fc462b84ef69cf070bb77fbe07c5e7648fcb585d..85574a1514cce1359ee125c1acb7771531584c2b 100644
--- a/media/blink/buffered_data_source.h
+++ b/media/blink/buffered_data_source.h
@@ -235,6 +235,11 @@ class MEDIA_EXPORT BufferedDataSource : public DataSource {
   // NOTE: Weak pointers must be invalidated before all other member variables.
   base::WeakPtrFactory<BufferedDataSource> weak_factory_;
 
+  // Disallow rebinding WeakReference ownership to a different thread by keeping
+  // a persistent reference. This avoids problems with the thread-safety of
+  // reaching into this class from multiple threads to attain a WeakPtr.
+  const base::WeakPtr<BufferedDataSource> weak_ptr_;
+
   DISALLOW_COPY_AND_ASSIGN(BufferedDataSource);
 };