Convert enable_bidirectional_stream into build flag local to net.

net/http/bidirectional_stream.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_HTTP_BIDIRECTIONAL_STREAM_H_
 #define NET_HTTP_BIDIRECTIONAL_STREAM_H_
 
 #include <stdint.h>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "net/http/bidirectional_stream_job.h"
 #include "net/http/http_stream_factory.h"
 #include "net/log/net_log.h"
+#include "net/net_features.h"
 
-#if !defined(ENABLE_BIDIRECTIONAL_STREAM)
+#if !BUILDFLAG(ENABLE_BIDIRECTIONAL_STREAM)
 #error Only include this if ENABLE_BIDIRECTIONAL_STREAM is defined
 #endif
 
 class GURL;
 
 namespace net {
 
 class HttpAuthController;
 class HttpNetworkSession;
 class HttpStream;
@@ skipping 174 matching lines @@
   // The underlying BidirectioanlStreamJob used for this stream. It is non-NULL,
   // if the |stream_request_| successfully finishes.
   scoped_ptr<BidirectionalStreamJob> stream_job_;
 
   DISALLOW_COPY_AND_ASSIGN(BidirectionalStream);
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_BIDIRECTIONAL_STREAM_H_