Extract ArcSupportMessageHost.

chrome/browser/chromeos/arc/ui/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_UI_ARC_SUPPORT_MESSAGE_HOST_H_
+#define CHROME_BROWSER_CHROMEOS_ARC_UI_ARC_SUPPORT_MESSAGE_HOST_H_
+
+#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);
+
+  // Register (or unregister if nullptr) the observer. Currently this class

[khmel, 2016/10/21 03:34:49]

nit: Register(s) unregister(s)

[hidehiko, 2016/10/21 07:40:28]

Good catch. Done in a new file.

+  // assumes that it has only one observer.
+  void SetObserver(Observer* observer);
+
+ private:
+  // Keep private. The instance will be created via Create().
+  ArcSupportMessageHost();
+
+  // Overrides NativeMessageHost:

[khmel, 2016/10/21 03:34:49]

nit: not sure, but 
// extensions::NativeMessageHost:
?

[hidehiko, 2016/10/21 07:40:27]

Hmm. There seem various patterns...
// $classname:
// Overrides $classname:
// $classname overrides:
// $classname override:
// Overridden $classname:

etc.
How about standardize "// $classname overrides:" then? I haven't touched to
other ones, but will do in a separate CL.

[Luis Héctor Chávez, 2016/10/21 07:50:48]

I'd consult the chromium-dev mailing list if this has already been discussed.
Otherwise, use the good old "whichever pattern has more matches with ag | wc -l
trick".

[hidehiko, 2016/10/21 10:06:13]

As long as this is not standardized, I'd like to make this off-topic.
I'm happy to change to any of above, and happy to have a discussion for
standardizing if necessary,
but I would like to avoid the discussion in this CL.

+  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_UI_ARC_SUPPORT_MESSAGE_HOST_H_