Close all writers before JingleSession is destroyed.

remoting/protocol/protobuf_video_writer.cc

Index: remoting/protocol/protobuf_video_writer.cc
diff --git a/remoting/protocol/protobuf_video_writer.cc b/remoting/protocol/protobuf_video_writer.cc
index 025445da5e920e224a32490478e47b8ca759b6fa..a03a4e696008e6697b3fc79ef6272421eb42b6f0 100644
--- a/remoting/protocol/protobuf_video_writer.cc
+++ b/remoting/protocol/protobuf_video_writer.cc
@@ -23,6 +23,10 @@ void ProtobufVideoWriter::Init(protocol::Session* session) {
   buffered_writer_->Init(session->video_channel(), NULL);
 }
 
+void ProtobufVideoWriter::Close() {
+  buffered_writer_->Close();
+}
+
 void ProtobufVideoWriter::ProcessVideoPacket(const VideoPacket* packet,
                                              Task* done) {
   buffered_writer_->Write(SerializeAndFrameMessage(*packet), done);