Introduce CancelUponDeferral() to buffered media loaders.

media/blink/buffered_data_source.cc

Index: media/blink/buffered_data_source.cc
diff --git a/media/blink/buffered_data_source.cc b/media/blink/buffered_data_source.cc
index e3e12e0f4dd553b44112ea7ec07a56bc0a6fb89f..bf93a001f0039972fcb56f3657099d1cce765b59 100644
--- a/media/blink/buffered_data_source.cc
+++ b/media/blink/buffered_data_source.cc
@@ -231,6 +231,12 @@ void BufferedDataSource::SetBitrate(int bitrate) {
                                     bitrate));
 }
 
+void BufferedDataSource::CancelUponDeferral() {
+  DCHECK(render_task_runner_->BelongsToCurrentThread());
+  if (loader_)
+    loader_->CancelUponDeferral();
+}
+
 void BufferedDataSource::Read(
     int64 position, int size, uint8* data,
     const DataSource::ReadCB& read_cb) {