Add TransportContext class.

remoting/host/cast_extension_session.cc

Index: remoting/host/cast_extension_session.cc
diff --git a/remoting/host/cast_extension_session.cc b/remoting/host/cast_extension_session.cc
index 1b8df914dee9adba2fb571bcde6ce0df778f3bb7..be71b1e7e668040d3fefa12fecf8c6055daace75 100644
--- a/remoting/host/cast_extension_session.cc
+++ b/remoting/host/cast_extension_session.cc
@@ -12,7 +12,7 @@
 #include "net/url_request/url_request_context_getter.h"
 #include "remoting/host/client_session.h"
 #include "remoting/proto/control.pb.h"
-#include "remoting/protocol/chromium_port_allocator_factory.h"
+#include "remoting/protocol/chromium_port_allocator.h"
 #include "remoting/protocol/client_stub.h"
 #include "remoting/protocol/webrtc_video_capturer_adapter.h"
 #include "third_party/libjingle/source/talk/app/webrtc/mediastreaminterface.h"
@@ -497,12 +497,13 @@ bool CastExtensionSession::InitializePeerConnection() {
   constraints.AddMandatory(webrtc::MediaConstraintsInterface::kEnableDtlsSrtp,
                            webrtc::MediaConstraintsInterface::kValueTrue);
 
-  rtc::scoped_refptr<webrtc::PortAllocatorFactoryInterface>
-      port_allocator_factory = protocol::ChromiumPortAllocatorFactory::Create(
-          network_settings_, url_request_context_getter_);
+  scoped_ptr<cricket::PortAllocator> port_allocator =
+      protocol::ChromiumPortAllocator::Create(url_request_context_getter_);
 
   peer_connection_ = peer_conn_factory_->CreatePeerConnection(
-      rtc_config, &constraints, port_allocator_factory, nullptr, this);
+      rtc_config, &constraints,
+      rtc::scoped_ptr<cricket::PortAllocator>(port_allocator.release()),
+      nullptr, this);
 
   if (!peer_connection_.get()) {
     CleanupPeerConnection();