Convert enable_bidirectional_stream into build flag local to net.

net/http/bidirectional_stream_job.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_JOB_H_
 #define NET_HTTP_BIDIRECTIONAL_STREAM_JOB_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "net/base/net_export.h"
 #include "net/socket/next_proto.h"
 
-#if !defined(ENABLE_BIDIRECTIONAL_STREAM)
-#error Only include this if ENABLE_BIDIRECTIONAL_STREAM is defined
-#endif
-
 namespace base {
 class Timer;
 }  // namespace base
 
 namespace net {
 
 class BoundNetLog;
 class IOBuffer;
 class SpdyHeaderBlock;
 struct BidirectionalStreamRequestInfo;
@@ skipping 101 matching lines @@
   // not associated with any stream, and are not included in this value.
   virtual int64_t GetTotalSentBytes() const = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(BidirectionalStreamJob);
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_BIDIRECTIONAL_STREAM_JOB_H_