mash: Add SystemTrayClient interface, use to show date settings

chrome/browser/ui/ash/system_tray_client.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_UI_ASH_SYSTEM_TRAY_CONTROLLER_MUS_H_
-#define CHROME_BROWSER_UI_ASH_SYSTEM_TRAY_CONTROLLER_MUS_H_
+#ifndef CHROME_BROWSER_UI_ASH_SYSTEM_TRAY_CLIENT_H_
+#define CHROME_BROWSER_UI_ASH_SYSTEM_TRAY_CLIENT_H_
 
 #include "ash/public/interfaces/system_tray.mojom.h"
 #include "base/macros.h"
 #include "chrome/browser/chromeos/system/system_clock_observer.h"
+#include "mojo/public/cpp/bindings/binding.h"
 
-// Controls chrome's interaction with the ash system tray menu.
-class SystemTrayControllerMus : public chromeos::system::SystemClockObserver {
+// Handles method calls delegated back to chrome from ash. Also notifies ash of
+// relevant state changes in chrome.
+class SystemTrayClient : public ash::mojom::SystemTrayClient,

[James Cook, 2016/09/24 00:34:37]

I combined the chrome -> ash and ash -> chrome communication into one class
because it's like SystemTrayDelegateChromeos. However, I could also keep the
chrome -> ash pieces in SystemTrayControllerMus (created at startup, connects to
ash on startup) and add a new SystemTrayClient (created on demand when ash
requests it). The latter approach might make the ChromeInterfaceFactory stuff a
little more like the other interfaces, but would introduce even more classes.

Do you have a preference?

[sky, 2016/09/26 15:23:14]

I actually prefer an explicit SetClient as it means less outgoing connections
from ash.

+                         public chromeos::system::SystemClockObserver {
  public:
-  SystemTrayControllerMus();
-  ~SystemTrayControllerMus() override;
+  SystemTrayClient();
+  ~SystemTrayClient() override;
+
+  static SystemTrayClient* Get();
 
  private:
+  // Connects or reconnects the |system_tray_| interface.
+  void ConnectToSystemTray();
+
+  // Handles errors on the |system_tray_| interface connection.
+  void OnClientConnectionError();
+
+  // ash::mojom::SystemTrayClient:
+  void ShowDateSettings() override;
+
   // chromeos::system::SystemClockObserver:
   void OnSystemClockChanged(chromeos::system::SystemClock* clock) override;
 
+  // System tray mojo service in ash.
   ash::mojom::SystemTrayPtr system_tray_;
 
-  DISALLOW_COPY_AND_ASSIGN(SystemTrayControllerMus);
+  // Binds the SystemTrayClient mojo interface to this object.
+  mojo::Binding<ash::mojom::SystemTrayClient> binding_;
+
+  DISALLOW_COPY_AND_ASSIGN(SystemTrayClient);
 };
 
-#endif  // CHROME_BROWSER_UI_ASH_SYSTEM_TRAY_CONTROLLER_MUS_H_
+#endif  // CHROME_BROWSER_UI_ASH_SYSTEM_TRAY_CLIENT_H_