Remove unnecessary posted task in cast_transport.cc.

extensions/browser/api/cast_channel/cast_transport.cc

Index: extensions/browser/api/cast_channel/cast_transport.cc
diff --git a/extensions/browser/api/cast_channel/cast_transport.cc b/extensions/browser/api/cast_channel/cast_transport.cc
index b3fe918505238d83b6a03540de2fb5913f52e414..04ab8f29532cea5d355d86afa7dc662a2f7b8c87 100644
--- a/extensions/browser/api/cast_channel/cast_transport.cc
+++ b/extensions/browser/api/cast_channel/cast_transport.cc
@@ -327,8 +327,6 @@ int CastTransportImpl::DoWriteCallback() {
   logger_->LogSocketEventForMessage(
       channel_id_, proto::MESSAGE_WRITTEN, request.message_namespace,
       base::StringPrintf("Bytes: %d", bytes_consumed));
-  base::ThreadTaskRunnerHandle::Get()->PostTask(FROM_HERE,
-                                                base::Bind(&base::DoNothing));
   base::ThreadTaskRunnerHandle::Get()->PostTask(
       FROM_HERE, base::Bind(request.callback, net::OK));