Decouple Blimp transport output from BlimpConnections using MessagePort.

blimp/net/message_port.h

Index: blimp/net/message_port.h
diff --git a/blimp/net/message_port.h b/blimp/net/message_port.h
new file mode 100644
index 0000000000000000000000000000000000000000..42d2603348a2e510a227f3c6ad405862540e1372
--- /dev/null
+++ b/blimp/net/message_port.h
@@ -0,0 +1,38 @@
+// Copyright 2016 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 BLIMP_NET_MESSAGE_PORT_H_
+#define BLIMP_NET_MESSAGE_PORT_H_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "base/supports_user_data.h"
+#include "blimp/net/blimp_net_export.h"
+
+namespace blimp {
+
+class PacketReader;
+class PacketWriter;
+
+// A duplexed pair of a framed reader and writer.

[Wez, 2016/08/20 00:09:10]

Suggest adding commentary to explain that we want to allow callers to associate
data with it, hence SupportsUserData.

Do you use the SupportsUserData for anything besides the StreamSocket based
impls? If not then I'd suggest switching the StreamSocket helper to just return
something derived from MessagePort, that owns the Socket. Or are you worried
about destructor ordering?

[Kevin M, 2016/08/22 21:50:46]

I just wanted to attach an object lifetime to MessagePort. I'll use an anonymous
namespaced subclass instead.

+class BLIMP_NET_EXPORT MessagePort : public base::SupportsUserData {
+ public:
+  MessagePort(std::unique_ptr<PacketReader> reader,
+              std::unique_ptr<PacketWriter> writer);
+  ~MessagePort() override;
+
+  PacketReader* reader() const { return reader_.get(); }
+  PacketWriter* writer() const { return writer_.get(); }
+
+ private:
+  std::unique_ptr<PacketReader> reader_;
+  std::unique_ptr<PacketWriter> writer_;
+
+  DISALLOW_COPY_AND_ASSIGN(MessagePort);
+};
+
+}  // namespace blimp
+
+#endif  // BLIMP_NET_MESSAGE_PORT_H_