Convert enable_bidirectional_stream into build flag local to net.

net/http/http_stream_factory_impl.cc

Index: net/http/http_stream_factory_impl.cc
diff --git a/net/http/http_stream_factory_impl.cc b/net/http/http_stream_factory_impl.cc
index e7d1ac34311b51abf7b5f8ea4c607f18946efa49..41b0fe6f0a7522cabf98cc1953636f20042f3d2b 100644
--- a/net/http/http_stream_factory_impl.cc
+++ b/net/http/http_stream_factory_impl.cc
@@ -14,11 +14,12 @@
 #include "net/http/http_stream_factory_impl_job.h"
 #include "net/http/http_stream_factory_impl_request.h"
 #include "net/log/net_log.h"
+#include "net/net_features.h"

[mmenke, 2016/01/04 21:50:36]

Why is this needed here, but not in, say,
net/http/http_stream_factory_impl_request.cc?  I had thought it was being
generated to include the define by the new rules, but maybe I was
misunderstanding things?

[mef, 2016/01/04 21:55:33]

I think your understanding matches mine. :) 
Without this include BUILDFLAG(ENABLE_BIDIRECTIONAL_STREAM) is triggering a
compilation error.
Which IMHO is a good thing.

It is not needed in net/http/http_stream_factory_impl_request.cc because it is
included in net/http/http_stream_factory_impl_request.h.

 #include "net/quic/quic_server_id.h"
 #include "net/spdy/spdy_http_stream.h"
 #include "url/gurl.h"
 
-#if defined(ENABLE_BIDIRECTIONAL_STREAM)
+#if BUILDFLAG(ENABLE_BIDIRECTIONAL_STREAM)
 #include "net/spdy/bidirectional_stream_spdy_job.h"
 #endif
 
@@ -91,7 +92,7 @@ HttpStreamRequest* HttpStreamFactoryImpl::RequestBidirectionalStreamJob(
   DCHECK(request_info.url.SchemeIs(url::kHttpsScheme));
 
 // TODO(xunjieli): Create QUIC's version of BidirectionalStreamJob.
-#if defined(ENABLE_BIDIRECTIONAL_STREAM)
+#if BUILDFLAG(ENABLE_BIDIRECTIONAL_STREAM)
   Request* request =
       new Request(request_info.url, this, delegate, nullptr, net_log,
                   Request::BIDIRECTIONAL_STREAM_SPDY_JOB);
@@ -306,7 +307,7 @@ void HttpStreamFactoryImpl::OnNewSpdySessionReady(
       // implementation is ready.
       NOTREACHED();
     } else if (request->for_bidirectional()) {
-#if defined(ENABLE_BIDIRECTIONAL_STREAM)
+#if BUILDFLAG(ENABLE_BIDIRECTIONAL_STREAM)
       request->OnBidirectionalStreamJobReady(
           nullptr, used_ssl_config, used_proxy_info,
           new BidirectionalStreamSpdyJob(spdy_session));