Extract ArcSupportMessageHost.

chrome/browser/chromeos/arc/ui/arc_support_message_host.cc

+// 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.
+
+#include "chrome/browser/chromeos/arc/ui/arc_support_message_host.h"
+
+#include "base/json/json_reader.h"
+#include "base/json/json_writer.h"
+#include "base/threading/thread_task_runner_handle.h"
+#include "chrome/browser/chromeos/arc/arc_auth_service.h"
+#include "chrome/browser/chromeos/arc/arc_support_host.h"
+
+namespace arc {
+
+// static
+const char ArcSupportMessageHost::kHostName[] = "com.google.arc_support";
+
+// static
+const char* const ArcSupportMessageHost::kHostOrigin[] = {
+    "chrome-extension://cnbgggchhmkkdmeppjobngjoejnihlei/"};
+
+// static
+std::unique_ptr<extensions::NativeMessageHost> ArcSupportMessageHost::Create() {
+  return std::unique_ptr<NativeMessageHost>(new ArcSupportMessageHost());
+}
+
+ArcSupportMessageHost::ArcSupportMessageHost() = default;
+
+ArcSupportMessageHost::~ArcSupportMessageHost() {
+  ArcAuthService* auth_service = ArcAuthService::Get();
+  if (auth_service)
+    auth_service->support_host()->UnsetMessageHost(this);
+}
+
+void ArcSupportMessageHost::SendMessage(const base::Value& message) {
+  if (!client_)
+    return;
+
+  std::string message_string;
+  base::JSONWriter::Write(message, &message_string);
+  client_->PostMessageFromNativeHost(message_string);
+}
+
+void ArcSupportMessageHost::SetObserver(Observer* observer) {
+  observer_ = observer;

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

nit: DCHECK(!observer_), meaning we cannot override previous observer

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

This also can be used to detach the observer. Added DCHECK but with different
condition.

+}
+
+void ArcSupportMessageHost::Start(Client* client) {
+  DCHECK(!client_);
+  client_ = client;
+
+  ArcAuthService* auth_service = ArcAuthService::Get();
+  if (auth_service)

[Luis Héctor Chávez, 2016/10/21 02:24:08]

This looks racy. If |auth_service| is null, then ArcAuthService will never be
able to get the MessageHost. What guarantees do we have that this will never
happen? Please comment about that and change this if to a DCHECK.

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

It seems ArcAuthService::Get() cannot be nullptr in this case.
DCHECK(auth_service)?
Previous realization had DCHECK() 

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

Indeed, here DCHECK is appropriate, but in dtor, if check is needed.
Added comment in dtor, and replaced this by DCHECK.

+    auth_service->support_host()->SetMessageHost(this);
+}
+
+void ArcSupportMessageHost::OnMessage(const std::string& message_string) {
+  if (!observer_)
+    return;
+
+  std::unique_ptr<base::Value> message_value =
+      base::JSONReader::Read(message_string);
+  base::DictionaryValue* message;
+  if (!message_value || !message_value->GetAsDictionary(&message)) {
+    NOTREACHED();
+    return;
+  }
+
+  observer_->OnMessage(*message);
+}
+
+scoped_refptr<base::SingleThreadTaskRunner> ArcSupportMessageHost::task_runner()
+    const {
+  return base::ThreadTaskRunnerHandle::Get();
+}
+
+}  // namespace arc