Implements ListenForSessionMessages in PresentationServiceImpl; uses Swap to avoid copying large da…

content/public/browser/presentation_session_message.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 CONTENT_PUBLIC_BROWSER_PRESENTATION_SESSION_MESSAGE_H_
+#define CONTENT_PUBLIC_BROWSER_PRESENTATION_SESSION_MESSAGE_H_
+
+#include <string>
+#include <vector>
+
+#include "base/memory/scoped_ptr.h"
+#include "content/common/content_export.h"
+
+namespace content {
+
+// Represents a presentation session message.
+// If this is a text message, data.size is 0; otherwise, message.size is 0.

[whywhat, 2015/05/01 15:26:12]

Why not one of the message/data is nullptr? Why not a union with an enum for the
type?
At least a method like isBinary() would be better than exposing this
implementation detail to the caller.

[haibinlu, 2015/05/01 19:03:20]

Done.

+struct CONTENT_EXPORT PresentationSessionMessage {
+  PresentationSessionMessage(const std::string& presentation_url,
+                             const std::string& presentation_id,
+                             scoped_ptr<std::string> message,
+                             scoped_ptr<std::vector<uint8_t>> data);
+  ~PresentationSessionMessage();
+
+  const std::string presentation_url;
+  const std::string presentation_id;
+  scoped_ptr<std::string> message;
+  scoped_ptr<std::vector<uint8_t>> data;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_BROWSER_PRESENTATION_SESSION_H_