Extract ArcSupportMessageHost.

chrome/browser/chromeos/arc/extensions/arc_support_message_host.h

+// 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 CHROME_BROWSER_CHROMEOS_ARC_EXTENSIONS_ARC_SUPPORT_MESSAGE_HOST_H_
+#define CHROME_BROWSER_CHROMEOS_ARC_EXTENSIONS_ARC_SUPPORT_MESSAGE_HOST_H_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "base/values.h"
+#include "extensions/browser/api/messaging/native_message_host.h"
+
+namespace arc {
+
+// Implements message routing to communicate with arc_support Chrome App.
+// Provides JSON (base::Value) APIs for the communication.
+class ArcSupportMessageHost : public extensions::NativeMessageHost {
+ public:
+  class Observer {
+   public:
+    // Called when an message is sent from arc_support Chrome App.
+    virtual void OnMessage(const base::DictionaryValue& message) = 0;
+
+   protected:
+    virtual ~Observer() = default;
+  };
+
+  static const char kHostName[];
+  static const char* const kHostOrigin[];
+
+  // Called when the arc_support connects the "port". Returns the
+  // instance of ArcSupportMessageHost.
+  static std::unique_ptr<NativeMessageHost> Create();
+
+  ~ArcSupportMessageHost() override;
+
+  // Sends a message to arc_support. If the client is not yet ready, the
+  // message will be just ignored.
+  void SendMessage(const base::Value& message);
+
+  // Registers (or unregisters if nullptr) the observer. Currently this class
+  // assumes that it has only one observer.
+  void SetObserver(Observer* observer);
+
+ private:
+  // Keep private. The instance will be created via Create().
+  ArcSupportMessageHost();
+
+  // extensions::NativeMessageHost overrides:
+  void Start(Client* client) override;
+  void OnMessage(const std::string& request_string) override;
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner() const override;
+
+  Observer* observer_ = nullptr;
+  Client* client_ = nullptr;
+
+  DISALLOW_COPY_AND_ASSIGN(ArcSupportMessageHost);
+};
+
+}  // namespace arc
+
+#endif  // CHROME_BROWSER_CHROMEOS_ARC_EXTENSIONS_ARC_SUPPORT_MESSAGE_HOST_H_